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.

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