Friday, June 29, 2012

Biological Science 15 (Evolution)


Day 26: 

Spoiler Alert 1: Evolution Exists
Spoiler Alert 2: Evolution, Not Tremendously Exciting
Evolution [1]

A. Evolution

The change of amount of alleles of genes within a population (yawn).

1. Natural Selection
The individuals that have traits that are extremely undesirable, don't survive to breed, so there are less of those undesirable traits as time goes on. Ex. Babies with hearts on the outside of their body.

A. Fitness Concept
From an evolutionary perspective reproduction is essential so, fitness means ability to live, mature and reproduce successfully. Homosexuals do not have high fitness from this perspective, though it is surprising how many homosexuals still produce children.

B. Selection by Differential Reproduction
Tendency towards reproduction is a trait that spreads, because individuals with a tendency not to reproduce do not spread their genes.

C. Concepts of Natural and Group Selection
Natural selection means those that survive to reproduce are "selected" to keep existing. Group selection explains Lemmings. In interest of group survival, the individual Lemming will migrate away (possible to their death) so the rest of the Lemmings have food.

D. Evolutionary Success as Increase in Percent Representation in the Gene Pool of the Next 

If an allele increases over time it is a "success." Diversity is actually a positive thing, that prevents disease. If it was good for an allele to increase to 100%, then it would have already happened. Gene flux is healthy... 

2. Speciation
Close entities are termed a species. Like humans, we are the Homo sapiens sapiens species.

A. Definition of Species
A species can interbreed, and naturally produce viable offspring (whales and dolphins breed, but their offspring are sterile).

B. Polymorphism
Different alleles. Red hair, brown hair, black hair. Blue eyes, amber eyes, grey eyes ext.

C. Adaptation and Specialization
Adaptation is the change in a population caused by natural selection. Specialization is adaptation to fit a certain niche (tall necks to eat leaves on tall trees).

D. Concepts of Ecological Niche, Competition
A niche is the place, food and resources that a species lives in and competes to occupy. Specialization allows a niche to be used by multiple species without competition. Ex. If a gas station and a restaurant are on the same corner they both use the corner without competing.  If two species use different niches they do not compete, if they use the same niche they do compete. Ex. If a Brazilian Jujitsu Gym and a Japanese Jujitsu Gym are on the same corner they compete for students, if they are in different areas they don't compete for students.

E. Concept of Population Growth Through Competition
Population growth slows down as food is less plentiful or due to competition for other resources like land or water. When a species is competing for food, members may begin to occupy different niches and become different species (like Darwin's Finches).

F. Inbreeding
Mating of relatives is known as inbreeding. Inbreeding decreases genetic diversity, making homozygotes more common (resulting in much higher risk of recessive diseases).

G. Outbreeding
Mating of non-relatives increases diversity and heterozygosity.

H. Bottlenecks, Genetic Drift
Bottlenecks are severe reductions of population size (thus genetic diversity). This happened to cheetahs, now they are practically clones. Genetic drift is random change (not selection) in allele frequency. When the population shrinks genetic drift is more pronounced.

I. Divergent, Parallel, and Convergent Evolution
Divergent (going different ways) evolution describes two species that used to be the same, but grew apart (producing homologous structures). Ex. food and healthy food were the same thing in the 1900s, but unhealthy changes were made to food and now food and healthy food are two separate things. Parallel (going the same way) evolution, the species were the same, grew differently, but now are staying similar and evolving in the same direction. Ex. Pop and country music have the same ancestor, they grew differently, but now they are not much different and headed in the same direction. Convergent evolution describes two species from different backgrounds that are becoming more similar. Ex. Cave animals all tend to loose color and vision.

J. Symbiotic Relationships
  • Parasites, do not have a symbiotic relationship, one species benefits to the detriment of the other.
  • Commensalism, do not have a symbiotic relationship, one species benefits.
  • Mutalism is a symbiotic relationship, both species benefit.

I. Parasitism
The host is harmed, the parasite benefits. Like tape worm, which takes nutrients from the host, causing damage and loss of nutrients.

Cestodes: Tape Worm [2]

II. Commensalism
The moss on tree is usually commensalistic. The tree allows the moss to have sunlight and a growing surface, but there is no benefit to the tree.

Giant Moss Trees [3]

III. Mutualism
The Famous Mutualism of Clownfish and Sea Anemones: the Clownfish fight off Butterfly Fish and the Sea Anemones protect the Clownfish from other predators. 

"I got your back Clownfish." "Good looking out Sea Anemone." [4]

3. Relationship Between Ontogeny and Phylogeny
Ontogeny is development during a lifetime of an individual. Phylogeny is the development of a species throughout evolutionary time. The human embryo goes through phases showing our phylogeny. We have gills, a notochord, segmentation, and flipper hands and feets, before we grow into our more familiar forms. 

Human Six Weeks Old [5]

4. Evolutionary Time as Measured by Gradual Random Changes in Genome
The molecular clock concept is that: random changes (drift) occur that are not caused by natural selection, measuring these changes tells how long ago two species diverged.

5. Origin of Life
Organic molecules created in the atmosphere shot out of the sky by a lightning bolt fell into the primordial ocean. Proved to be possible by Urey-Miller's experiment (they had gas, a spark and water in a closed system and the system turned pink and grew amino acids). [6]

Gas + Spark + Water -> Life As We Know It

RNA formed. RNA became enveloped. Anaerobic heterotrophs existed first (there was no oxygen or light), then anaerobic autotrophs started photosynthesizing (creating oxygen), last the aerobs evolved because there was now oxygen. Eukaryotes evolved by engulfing small mitochondria or chloroplasts. [7]

B. Comparative Anatomy

The primitive vertebrae defines humans as chordates, the advanced vertebrae as vertebrates.

1. Chordate Features
The phylum chordate has a notochord (backbone), pharyngeal pouches (cheeks), brachial arches (forming gill slits).

A. Notochord
The notochord is a primitive spine, not yet made of bone.

B. Pharangeal Pouches, Brachial Arches
Together pharangeal pouches and brachial arches form gill slits (which rare people retain).

C. Dorsal Nerve Cord
The dorsal (on the back) nerve cord forms the spine and the brain.

2. Vertebrate Phylogeny (Vertebrate Classes and Relations to Each Other)
The group vertebrate have spines. 

Vertebrates start with fish:

  • Agnatha (jawless): eel-like.
  • Condrichthyes: like sharks and rays having jaws and skeletons (of cartillage).
  • Osteichthyes (bony): feeder fish having a bony skeleton.
  • Amphibians: the bony skeleton was strong enough to support weight on land.
  • Reptiles: can go away from water (without drying out), lay eggs.
  • Mammals: milk, hair and heterodontic teeth. AND Birds: still lay eggs, feathers, beaks.  [7]

Foot Notes:
1. Gomez, R. Evolution. Drawing. [Online]. 2012. (retrieved Jul 03, 2012)

2. Tape Worms Attached to Stomach Wall. Photograph. Ewwwww! My Pet Has Tape Worms! [Online]. 2009. (retrieved Jun 29, 2012).

3. Giant Moss Tree. Photograph. Pics of Trees. [Online]. (retrieved Jun 29, 2012).

4. Clown Fish and Sea Anemone. Photograph. Christian Brothers University. [Online]. (retrieved Jun 29, 2012).

5. Human Six Weeks Old. Photograph. Precious Moments After "I Do."  [Online]. Feb 13, 2012. (retrieved Jun 29, 2012).

6. Miller-Urey Experiment. Wikipedia. [Online]. Jun 27, 2012. (accessed Jul 03, 2012).

7. Evolution. [Online]. 2008. (accessed Jun 29, 2012).

Biological Science 11 (Respiratory System)

Biological Science 11 (Respiratory System)

Day 20:

A. Respiratory System
The respiratory system works with the cardiovascular system, to supply the oxygen needed for cellular respiration, which creates the energy necessarily for human life (ATP).

1. General Structure and Function
The respiratory system takes air from the environment, warming it in the nose or mouth (nasal or oral cavities), moistening it and filtering pathogens out of it in the pharynx (throat), the air travels into the larynx (voice box), the trachea (wind pipe), the bronchi of the lung (left or right), down smaller and smaller tubes, into the aveoli where the oxygen in the air is passed into the capillaries in return for waste carbon dioxide (which begins the reverse path to the outside environment).

The Respiratory System

A. Gas Exchange, Thermoregulation
The oxygen is exchanged for carbon dioxide, between the alveolar sacs and capillaries. Thermoregulation by the respiratory system occurs due to heat loss (due to exhaling warm air).

The diffusion of oxygen follows Henry's law, that states an equilibrium constant of the dissolved amount of oxygen is proportional to the partial pressure of the oxygen just above the surface of the solution.

B. Protection Against Disease, Particulate Matter
The nose hair grabs large particles and sweeps them out of the respiratory track along with mucus. Thin cilia help move particles out of the respiratory track. Healthy alveoli have white blood cells (macrophages) to kill invaders.

2. Breathing Mechanisms
The act of breathing out is effortless, since the atmosphere has less pressure then our full lungs, air rushes out. Breathing in requires contraction of the diaphragm. The concept is called negative pressure breathing.

A. Diaphragm, Rib Cage, Differential Pressure
The diaphragm is a dome shaped muscle that helps the lungs expand. The rib cage has muscles (the external and internal intercostals) that also help with breathing. The rib cage usually keeps the lungs from collapsing. Our lungs always have a pressure that keeps them from collapsing. Airflow follows lower pressure.

B. Resiliency and Surface Tension Effects
Healthy lungs are elastic, springing back after each breath. Too much surface tension would collapse the lung's air sacks (alveoli), surfacant (soap) produced by the lung, keeps this from happening. In emphysema the surfacant is missing and many air sacks collapse making breathing very strenuous (like checking out at a big store with only one cashier left).

Thursday, June 28, 2012

Biological Science 10 (Muscle and Skeletal Systems)

Muscle and Skeletal Systems

Day 19:

Muscle and Skeletal Systems
McGraw Hill

A. Muscle System

1. Functions
The muscle of the body is more important them just movement, also support and protection, driving blood flow, driving digestion, tramping and generating heat and also facial expressions and body language.

A. Support, Mobility
The bones are cushioned by muscle, joints are stabilized by muscle, shortening of muscle pulls bones causing mobility.

B. Peripheral Circulatory Assistance
The main way for veins to return blood to the heart is by muscles squeezing the blood vessels. So if people don't get much exercise blood flow in the limbs is poor, therefore lymph flow in the limbs is very poor and many disease arise (such as peripheral vascular disease).

C. Thermoregulation (Shivering Reflex)
The arrector pilli muscles can generate a lot of heat by contracting (known as shivering).

2. Structural Characteristics of Skeletal, Smooth, and Cardiac Muscle; Striated versus Nonstriated
Both skeletal and cardiac muscle are striated (have stripes); Smooth muscle is solid. Booth smooth muscle and cardiac muscle are involuntary and have a single nucleus; skeletal muscle is voluntary and multinucleated. Smooth muscle is "eye" shaped, cardiac muscle is branched or "Y" shaped, skeletal muscle is "l" shaped/straight. Cardiac tissue has automautaticity, it can beat on it's own apart from the body (even a small piece of heart tissue can beat on its own outside the body).

Cardiac Tissue Automautaticity (Rat Heart)

3. Nervous Control
The muscles are always controlled by nerves, even during a reflex arc (even when the brain is not signaling the muscles, the nerves still do).

A. Motor Neurons
The motor neurons cause motion or other effects. Also called efferent neurons. They are the actuators of the body. Somatic motor neurons provide conscious control of the skeletal muscles. The autonomic motor neurons provide unconscious control of both smooth and cardiac muscle.

B. Neuromuscular Junctions, Motor End Plates
The small gap between a neuron and a muscle is aptly named, the neuromuscular junction. Here the axon terminal sends neurotransmitters to the motor end plate/sarcolemma, triggering a release of calcium that causes muscle contraction.

C. Voluntary and Involuntary Muscles
The voluntary muscles are skeletal. The involuntary muscles are smooth and cardiac muscle.

D. Sympathetic and Parasympathetic Innervation
The sympathetic nervous system is in response to stress, threat or exercise (faster heart rate, pupil dilation, increased blood pressure, increased blood to muscles). The parasympathetic nervous system is in response to relaxation, digestion or sleep (slower heart rate, pupil constriction, lower blood pressure, and increased blood to digestive organs). 

B. Skeletal System

The skeleton does more then provide a frame for movement, it is a living tissue that creates blood, helps the immune system, stores calcium, fat and other minerals, protects

1.  Functions
The main functions are: support, protection, blood production and calcium storage.

A. Structural Rigidity and Support
The bones are made of a calcium salt crystal. Compact bone is very rigid allowing it to bear weight. Bone has a lattice structure that is strengthened by exercise, especially weight lifting.

B. Calcium Storage
Bones store calcium. Calcitonin puts calcium in, parathyroid takes calcium out of the bones.

C. Physical Protection
The internal organs are protected by the ribs and sternum, the brain is protected by the skull and the spinal cord is protected by the vertebrae.

2. Skeletal Structure
The adult has 206 bones. Many were fused together like the sacrum. 

The Skeleton Typogram
Aaron Kuehn

A. Specialization of Bone Types; Structures
The types of bones include: long bones (the humerus/arm and femur/leg), short bones (the carpal/wrist bones), flat bones (the cranium/skull, scapula/shoulder, costals/ribs), irregular bones (the vertebrae/spine, the pelvic bones/the hip) and seasamoid bones (within a tendon ex. patella/knee cap).

B. Joint Structures
The joints are the weak points of the body (exploited by jiu jitsu for weaker fighters to control stronger opponents), where bones connect allowing motions. All joints are slightly movable (craniosacral massage moves the skulls sutures, which actually move on their own too). Joints are called non-mobile (synarthrotic), when they move very little (usually connect bones with cartilage or fibrocartilage). Mobile joints (diarthrotic) contain synovial fluid to lubricate the bones. This fluid is kept in bursae, sacks that will burst under too much pressure trying to save the joint by giving it maximum lubrication when it is being overstretched (like during an armbar). 

  • Ball and socket joints/enarthrosis (hip and shoulder) have the most motion. 
  • Hinge joints/ginglymus (elbow and knee) only have motion across one plane.
  • Gliding joint/arthrodial joint (acromioclavicular joint, wrist joints) allow gliding/sliding.
  • Pivot joints/trochoid joint (radioulnar joints, atlanto-axial joint) allow rotation.
  • Condyloid joints/ellipsoidal joint (metacarpophalangeal joints, metatarsophalangeal joints) permit motion across two planes. 
  • Saddle joints/sellar joints (thumb and sternoclavicular joint) have motion across two planes. One side in convex the other concave.

C. Endoskeleton versus Exoskeleton
The endoskeleton (within skeleton) is what humans have. The exoskeleton (outside skeleton) is what aliens, predators, insects and lobsters have. Exoskeletons are usually chitin.

3. Cartilage (Structure, Function)
The cells are chondrocytes, the cells are scattered around a gel (matrix) that has fiber in it. It is squishy due to the matrix, flexible and tough due to the fibers (elastic and collagen). Cartilage functions in protecting bone ends from damage and supporting the vertebrata from shock. This tissue is avascular meaning no blood, it required movement to squish nutrients into its matrix and toxins out. Movement is essential for joint health.

4. Ligaments, Tendons
The ligaments (link bone to bone) and tendons (tie bone to muscle) are made of tough bands of connective tissue. Avascular are well. Tendons contain Golgi body receptors that let the body know when the tendon is being stretched. 

5. Bone Structure
There are two types of bone structure, compact (looks like tree stumps) and cancellous bone (looks like lace). The membrane of a bone is called periosteum (containing stem cells). Marrow, blood vessels and nerves run down the center of lone bones. The cells are known as osteocytes. 

A. Calcium–Protein Matrix
The martix is calcium salt, collagen fibers and a gel like ground substance.

B. Bone Growth (Osteoblasts, Osteoclasts)
Osteoblasts make bone. Osteoclasts destroy bone. Longitudinal growth is height, appositional growth is width.

Wednesday, June 27, 2012

Biological Sciences 9 (Digestive and Excretory Systems)

Digestive and Excretory Systems

Day 17:

A. Digestive System

Food gets chewed up, becoming a bolus, then it gets swallowed passes through the pharynx, transported down the esophagus by peristalsis, into the stomach where it is churned, through the pyloric sphincter into the small intestines (the duodenum) where enzymes from the liver and gallbladder break the food down into nutrients that are absorbed in the small intestines, feces pass through the large intestines where water is removed and then pass out of the body.

The Digestive System

1. Ingestion
Food in the mouth starts getting converted to starch and glucose by amylase.

Review of the Digestive System

A. Saliva as Lubrication and Source of Enzymes
The saliva dissolves food into starch and glycogen with amylase. The mucin in saliva helps lubricate the bolus (chewed food). Saliva contains antibodies and lysozyme to kill pathogens.

B. Epiglottal Action
The epiglottis helps cover the trachea so food doesn't get into the lungs.

C. Pharynx (Function in Swallowing)
The pharynx (the throat) is between the mouth and esophagus. The pharynx swallows food, allowing food into the esophagus.

D. Esophagus (Transport Function)
The esophagus is the tube that food travels through on the way to digestion. Food is helped through be peristalsis. 

2. Stomach
The stomach helps break food down so by the time food gets to the small intestines, it can be absorbed.

A. Storage and Churning of Food
The stomach has a lot of room to store and churn a meal. The stomach stretches when it is full.

B. Low pH, Gastric Juice, Protection by Mucus Against Self-Destruction
The pH is usually very low in the stomach (due to parietal cells secreting HCl). The cheif cells secrete pepsin and the enteroendocrine cells secrete hormones. The stomach has a lining of mucus protecting it. 

C. Production of Digestive Enzymes, Site of Digestion
The stomach produces pepsin, which digests protein at a low pH. The stomach also churns food.

D. Structure (Gross)
The stomach has a fundus, body and antrum draining into the deuodenum via the pyloric sphincter.

The Stomach

3. Liver
The liver is the largest gland in the body.

A. Production of Bile
The liver makes bile from cholesterol, bile then gets stored in the gallbladder and then empties into the small intestines to break down fat.

B. Roles in Nutrient Metabolism, Vitamin Storage
The liver makes glycogen from glucose
Gluconeogenisis from glycerol and amino acids (deamination)
Breaks down fats to make cholesterol
Makes lipoproteins used to transport fats
Stores iron and vitamins A, D and B12

C. Roles in Blood Glucose Regulation, Detoxification
If the blood sugar is low the liver regulates it through glucogenesis; too high glycogeneis. The liver detoxifies the body by removing toxins and drugs, metabolizes alcohol, and removes ammonia from the blood.

D. Structure (Gross)
The liver has a large right lobe and a small left lobe.

The Liver

4. Bile
Bile breaks down fat.
A. Storage in Gallbladder
Bile is formed in the liver, stored in the gallbladder and released when needed to break down fat.

B. Function
Bile breaks down fat by emulsifying it (not enzymaticly), making micelles to increase surface area for lipase action.

5. Pancreas
The pancreas makes most digestive enzymes. Amylase brakes down starch. Lipase breaks down fat. Ribonuclease breaks down nucleic acids. The pancreas also make bicarbonate (HCO3-) and proteases. The islets of Langerhans have four cell types α, β, δ and PP cells. α cells make glucagon, β cells make insulin, δ make somatostatin and PP cells make pancreatic polypeptide.

A. Production of Enzymes, Bicarbonate
The pancreas neutralized stomach acid by releasing bicarbonate ions into the small intestines/duodenum, so the enzymes there can work at their preferred pH of 7.

B. Transport of Enzymes to Small Intestine
The pancreas transports digestive enzymes to the small intestines via a duct, therefore the pancreas has an exocrine function.

C. Structure (Gross)
The pancreas lays under the stomach and drains into the small intestines.

The Pancreas

6. Small Intestine
The small intestines absorbs most of the nutrients and reabsorbs most of the water. Therefore after drinking alcohol, people don't feel the full effect until the alcohol reaches the small intestines and is absorbed by the body. 

If you said pseudomyxoma peritonei syndrome with a tumor on the greater omentum and transverse colon... good job.

A. Absorption of Food Molecules and Water
The food is absorbed into the cell and given to the bodies capillaries (except fat, fat goes into lacteals). Active transport is needed since there is a lot of food in the red blood cells, but they try to absorb even more food still, in order to distribute it among the body.

B. Function and Structure of Villi
The small intestines have finger like projections (villi and microvilli) giving them more surface area to absorb food. 

C. Production of Enzymes, Site of Digestion
The small intestines absorbs most of the nutrients and drinks most of the water. 

*The small intestines make protease and amylase.

D. Neutralization of Stomach Acid
*The pancreas neutralized stomach acid by releasing bicarbonate ions into the small intestines, so the enzymes there can work at their preferred pH of 7.

E. Structure (Anatomic Subdivisions)
The small intestines structure consists of the duodenum, the jejunum and the ileum. 

The Small Intestines

7. Large Intestine
The small intestine takes in most of the nutrients, the large intestine absorbs water and stores feces. The regions of the large intestines are cecum (appendix is here), ascending colon, transverse colon, descending colon, sigmoid colon and rectum.

The Large Intestines

A. Absorption of Water
The large intestines absorbs water the small intestine missed, some water remains in the waste in a healthy digestive track.

B. Bacterial Flora
The good bacteria in the gut ferment undigested nutrients resulting in carbon dioxide gas and also produce vitamin K. 

C. Structure (Gross)
The large intestine does not absorb as much nutrients as the small intestine, therefore there are no villi.

The Large Intestines

8. Rectum (Storage and Elimination of Waste, Feces)
Other then smuggling things into prison or transporting drugs, the rectum also stores feces, during defecation the sphincter relaxes and feces are passed, mostly by gravity.

9. Muscular Control
Muscular control of the digestive system is a pleasant thing to have. Yoga can teach people how to help move their digestive system in a helpful way, I learned how to do that in Brazil (DeRose Method). 

A. Sphincter Muscle
Sphincter muscles of the digestive track include, the gastroesophageal (cardiac) sphincter between the esophagus and stomach, the pyloric sphincter between the stomach and small intestine and the anal sphincter.

B. Peristalsis
A rhythmic squeezing of the intestines, by smooth muscle cells to move food along. 

Day 18:

B. Excretory System

The kidneys, urinary track and surrounding arteries and veins form the renal  or excretory system.

1. Roles in Homeostasis
The kidneys control fluid balance (controlling blood pressure, pH and many ions such as sodium, chloride, potassium, calcium,m and phosphate).

A. Blood Pressure
The kidneys can keep water (by reabsorbing water or making less urine) or shed water (by reabsorbing less water or creating more urine), thus affecting the total vascular pressure.

Low Blood Pressure: 

  • Renin is released, forming angiotensin II, stimulating aldosterone release from the adrenal glands, which raises blood pressure by causing the distal tubules in the kidney to reabsorb more Na+ (which leads to more water reabsorption). 
  • Antidiuretic Hormone released from storage in the pituitary, causes more water reabsorption in the distal kidney tubules, which raises blood pressure. Vasoconstriction also occurs causing less fluid to go into the kidney tubules.

High Blood Pressure: 

  • Atiral natriuertic peptide is released by the heart, causing vasodilation and more excretion of  Na+ and water (in the kidney).

B. Osmoregulation
The kidneys can control how much re-absorption of ions occurs in the tubules. 

Blood plasma is mainly Na+ and Cl-Na+ and Clare the main determining factors of osmoregulation. K+ and Ca2+ are also regulated by the kidneys. Aldosterone causes K+to be excreted in the urine as Na+  is retained. Calcium and phosphate are regulated by parathyroid hormone. Parathyroid hormone causes reabsorption of Ca2+ in the kidneys.

C. Acid–Base Balance
The kidneys can keep or shed bicarbonate to control pH.

CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-

D. Removal of Soluble Nitrogenous Waste
The kidneys turn nitrogenous waste into urine.

Amino acids are made into ammonia, which is made into urea and exits the body.

2. Kidney Structure
A pair of bean shaped organs that eliminate waste by filtering the blood of toxins, waste and excess. They regulate fluid balance. There are more then a million nephrons in each kidney.

Kindey Structure and Overview

A. Cortex
The outer part of the kidney, where there are convoluted tubules.

B. Medulla
The inner part of the kidney, where the loop of Henle exists.

3. Nephron Structure
The nephron is the functional unit of the kidney, where blood fluid gets filtered. Afferent arterioles drain fluid into the bowman's capsule, fluid travels down the proximal tubule, into the loop of Henle, through the distal tubules and into a collecting duct shared by other nephrons (by that time the fluid is urine).

A. Glomerulus
The glomerulus is a collection of fenestrated capillaries.

B. Bowman’s Capsule
The bowman's capsule ensheaths the glomerulus.

C. Proximal Tubule
The next to the bowman's capsule is the proximal convoluted tubule, where reabsorption of nutrients, salt and water takes place. Secretion takes place also. 

D. Loop of Henle
The loop of Henle is where the countercurrent multiplier mechanism occurs. In the descending limb water is reabsorbed, in the ascending limb salt is reabsorbed. 

E. Distal Tubule
The distal convoluted tubule reabsorbes salts and water and secretes K+. The amount of reabsorption is controlled by hormones. 

amount of secretion is controlled by aldosterone.

F. Collecting Duct
The urine of many nephrons collects in the same duct. Like a sewer drains sewage from many houses. Antidiuretic hormone can affect reabsorption of water or salt in the collecting duct.

4. Formation of Urine
The formation of urine, out of blood, is what rids the body of toxins that enter in the food or are a byproduct of living reactions. This mechanism is damaged for people of dialysis or with renal failure. High blood pressure and diabetes impair kidney function.

A. Glomerular Filtration
The fluid pressure of blood pushes anything small enough to fit through the fenestrations of the capillaries into the nephrons. 

B. Secretion and Reabsorption of Solutes
The goal of secretion is to rid the body of creatinine and uric acid. The goal of reabsorption is to keep the body's water, ions and nutrients. 

C. Concentration of Urine
The distal convoluted tubes all carry urine, which becomes more concentrated in the collecting duct. The loop of Henle's high concentration is what drives reabsorption of water in the collecting duct.

D. Countercurrent Multiplier Mechanism (Basic Function)
Using an NaCl pump on the ascending limp of the loop of Henle, a concentration gradient is made allowing urine to become concentrated in the collecting duct. The countercurrent is, the descending limb (water flows out, salt stays constant) and the ascending limb (salt flows out, water stays constant).

5. Storage and Elimination (Ureter, Bladder, Urethra)
The kidneys send waste through the ureters into the bladder (made of transitional epithelium to allow expansion), from there urine goes through the urethra to exit the body.