When the external environment changes drastically, the body uses various mechanisms to maintain internal systems.
Detecting and Responding to Changes in the Environment
Negative feedback (most common): The results of a process inhibit that very process.
Example: Body temperature.
Stimulus: hot weather → body temp rises.
Response: produce sweat.
Result: temp returns to normal.
Stimulus: cold weather → body temp falls.
Response: goose bumps (raise body hairs to trap warmth).
Result: temp returns to normal.
Body Temperature Regulation
Ectotherms
Get their heat from the environment.
Sometimes called “cold-blooded”.
Examples: Invertebrates, fishes, amphibians, and reptiles.
Endotherms
Generate body heat internally.
Sometimes called “warm-blooded”.
Examples: Mammals and birds.
Four Primary Mechanisms for Regulating Body Temperature
Physical (anatomical).
Behavioral.
Physiological.
Cellular.
Examples of Ways to Regulate Body Temp
Physical Methods:
The walrus has a thick coat of blubber that provides insulation from the external environment.
Behavioral Methods:
The African ground squirrel shades itself with its tail while foraging, to minimize heat from the sun.
Physiological Methods:
By panting, dingos make use of the efficient loss of heat due to evaporation.
Cellular Methods:
Human infants have a special type of fat that produces heat, rather than ATP, when broken down.
Diabetes
An example of a breakdown in homeostasis.
The body fails to produce enough insulin (type 1) or target cells do not respond normally (type 2).
Causes:
Genetic.
Environmental.
Results:
Liver/kidney damage.
Blindness.
Amputations.
Significant contributor to 25% of deaths.
Positive Feedback
A form of regulation in which the results of a process intensify that same process.
Example: Childbirth.
Hormones stimulate uterine contractions.
Contractions stimulate the release of more hormones.
Result: more contractions.
The Digestive System
A continuous tube that runs from the mouth to the anus
Tube is called the Alimentary Canal
Alimentary Canal
The mouth, also called the oral cavity, is the site of ingestion.
The section at the back of the mouth is called the pharynx
The pharynx splits into two tubes
Esophagus: leads to the gut.
Trachea leads to the lungs.
The epiglottis moves to cover the entrance to the trachea, directing food down the esophagus.
Food Processing – Four Stages
Ingestion (eating).
Digestion (mechanical and chemical).
Absorption (primarily by cells lining the small intestine).
Elimination.
Digestion
Mechanical digestion (mostly chewing) is the use of physical processes to break down food into smaller pieces.
Chemical digestion is the use of enzymes to perform hydrolysis, chemical reactions that use water to break bonds within large molecules.
Chemical Digestion
Occurs in the mouth, stomach and intestines
Food moves through the gut through contractions called peristalsis.
Cells lining the stomach secrete gastric juice, containing enzymes (such as pepsin) and acids.
Sphincter muscles closes the stomach after food enters, preventing back-flow of stomach acids into the esophagus.
Another sphincter closes the stomach from the small intestine.
Food particles are called "Chyme"
Gastric Bypass Surgery
Surgery makes the stomach smaller.
Food "bypasses" most of the stomach and part of the small intestine
Chemical Digestion in the Small Intestine
The small intestine is all about maximizing surface area for absorption of nutrients:
Length, villi, and microvilli
SMALL INTESTINE
20 feet long with many folds
VILLI
Finger-like projections that line the small intestine
MICROVILLI
Thread-like projections that line cells in the villi
The surface area of the small intestine is equivalent to a TENNIS COURT!
Digestion Completion
Digestion is completed in the small intestine, at which point carbohydrates, proteins, and fats have been broken down into simple sugars, amino acids, and fatty acids.
Colon (large intestine)
The remaining chyme—mostly indigestible materials—leaves the small intestine and enters the large intestine, or colon.
Water, salts, and some vitamins are absorbed.
The colon ends in a chamber called the rectum.
A storage compartment for the feces (mostly, indigestible parts of consumed food).
Symbiotic bacteria produce vitamins and aid in digestion
Diseases that effect the intestines
Celiac and Chron’s Disease– autoimmune disease that effects the intestines
Accessory Organs
Accessory organs secrete specific digestive chemicals into the alimentary canal via ducts.
Salivary glands: Secrete enzymes that break down starch (a carbohydrate).
Liver: Secretes bile for breaking up fats.
Gall bladder: Stores bile.
Pancreas: Secretes lots of digestive enzymes.
Illnesses of the Digestive System
Common ailments include:
Acid reflux
Gallstones
Constipation
Appendicitis
Cholera
Inflammatory bowel disease
Ulcer
Food For Thought
Is it possible for a person to be both obese and malnourished