1

Homeostasis &

The Digestive System

Hungry???

2

Nutritional requirementsAnimals are heterotrophs

need to take in foodWhy? fulfills 3 needs…

fuel = chemical energy for production of ATP raw materials = carbon sources for biosynthesisessential nutrients = substances animals cannot

make themselves• elements (N, P, K, Fe, Na, K, Ca, etc.), NAD, FAD, etc.

3

Energy budget

food intake

ATPproduction

biosynthesis

• basal (resting) metabolism

• activity• temperature

regulation

• growth• reproduction

{{

storage• glycogen• fat{

4

A body functions properly only when the needs of the organisms (water, food, heat, oxygen and pressure) remain within the narrowly required limits.

Homeostasis: The tendency to maintain a stable internal environment.Ex: Furnace and air conditioner unit to maintain

constant temperature

5

Negative feedback mechanism:Negative feedback occurs when an increase in

some factor is sensed and is lowered

A response the body has to an occurrence that disturbs the homeostasis of the body. As the body reacts to that occurrence and moves closer to homeostasis, the receptors are shut down, thus causing fewer effectors to produce a product that’s needed to bring the body back to homeostasis, in the end having a “negative” effect on the production. The purpose of this is to stop overproduction or overreaction.

6

Homeostatic mechanism in regulating body temperature:

Shivering – in a cold environment muscles will contract involuntarily producing heat

Sweating - in an overheated environment the brain triggers a changes that promotes the increased loss of body heat

7

Managing glucose levelsHuman body regulates the use & storage of

glucose, a major cellular fuel insulin reduces blood glucose levels

when glucose levels rise above set point, pancreas secretes insulin

promotes transport of glucose into cells & storage of glucose as glycogen in liver & muscle cells

dropping blood glucose levelsglucagon increases blood glucose levels

when glucose levels drop below set point, pancreas secretes glucagon

promotes breakdown of glycogen & release of glucose into the blood

increasing blood glucose levels Show PDF of insulin

8

• Regulation: Maintaining Homeostasis Balancing glucose levels in blood

pancreas

pancreas

insulin

glucose storage

glucose uptake

glucose release

depress appetite

stimulatehungerglucagon

9

Essential Nutrients

What happens if an animal’s diet is missing an essential nutrient?deficiency diseases

scurvy — vitamin C (collagen production)rickets — vitamin D (calcium absorption)blindness — vitamin A (retinol production)anemia — vitamin B12 (coenzyme function)

kwashiorkor — protein deficiency

10

DigestionThe reduction of large food molecules into

smaller absorbable units and conversion of insoluble units into soluble ones.

This is accomplished by mechanical action, chemical and enzymatic action.

Enzymes are synthesized by cells in the mouth, stomach, pancreas and small intestine

11

Normally 92- 95% of a diet is digested and absorbed, but the process varied for each nutrient

http://www.ama-assn.org/ama/pub/category/7155.html

12

Types of digestive action

MechanicalMovement of the teeth grinding the food in the

mouth

ChemicalChanging the food molecules into new and

different moleculesLipids Lipase Fatty acids + glycerol

13

Alimentary Tract

Alimentary canalA muscular tube about 9 meters long

Appendage organs include:Liver, biliary tree and pancreas

Extends from the mouth to the anus

Receives food . . . Digestion/absorption occurs . . .transport to cells . . .excretion of waste

14

Diagram of Alimentary canal

Peristalsis – propelling movements which are a forward motion that is wavelike

Peristalsis pushes tubular contents ahead of it through the alimentary canal

15

MouthTeeth mechanically grind and crush food

Saliva moistens and binds food mass

Salivary amylase begins digestion of starch

Chewed food mass bolus

Passes from mouth into esophagus

Movement is controlled by peristalsis

16

Approximately 1.5 liters of saliva are produced daily by salivary glands (~ 6 cups) Figure 12.1

Amylase is a digestive enzyme It splits starch and glycogen (both carbohydrates) into

disaccharides via hydrolysis

Mucus binds food particles and acts as a lubricant in swallowing

Esophagus – straight tube that provides a passageway between the pharynx and stomach

17

Stomach

Chemical digestion begins in the middle of the stomach mixing food with gastric juices

Gastric juices contain HCl, intrinsic factor, pepsinogen, gastric lipase & mucus

Food becomes semi-liquid chyme (50% water)

Stomach is emptied in 1 – 4 hoursSphincter–valves at either end of stomach

18

The lining of the stomach is covered with numerous small holes. These are the openings of gastric pits which extend into the mucosa forming gastric glands.

19

Stomach helps to initiate the digestion of proteins, but also helps speed up the digestion of carbohydrates and fatsPepsin is the most important digestive enzyme

in the stomachPepsin is a protein-splitting enzyme

It carries on a limited amount of absorption

20

The pyloric sphincter (pylorus) is a muscle that acts as a valve to prevent regurgitation of food from intestines back into the stomach

21

Rugae: thick folds in stomach wall

22

Pancreas

Functions as an endocrine glandReleases hormones

Functions as an exocrine glandSecretes digestive juicesPancreatic juices move into the intestine

(duodenum)

Contains enzymes that digest carbohydrates, fats, proteins and nucleic acids

23

Viewing the digestive system in the anatomical position, the pancreas is found in under the stomach in the left hypochondriac & epigastric regions

24

Liver

Located below the diaphragm in the right hypochondriac and epigastric regions of the abdominal area.

25

26

The liver metabolizes carbohydrates lipids and proteins

Stores glycogen, vitamins A, D, B12 and iron

Filters blood Detoxifies bloodSecretes bileAn Introduction to the Liver – PDF File

27

Other functions of the liver Producing quick energy when it is needed;  Manufacturing new body proteins;  Preventing shortages in body fuel by storing certain vitamins, minerals, and

sugars;  Regulating transport of fat stores;  Regulating blood clotting;  Aiding in the digestive process by producing bile;  Controlling the production and excretion of cholesterol;  Neutralizing and destroying poisonous substances;  Metabolizing alcohol;  Monitoring and maintaining the proper level of many chemicals and drugs in

the blood;  Cleansing the blood and discharging waste products into the bile;  Maintaining hormone balance;  Serving as the main organ of blood formation before birth;  Helping the body resist infection by producing immune factors and by

removing bacteria from the bloodstream;  Regenerating its own damaged tissue; and  Storing iron.

28

Bile - Yellowish, green liquid made of bile salts, bile

pigments, water, cholesterol and electrolytes

Bile salts aid the digestive enzymes and enhance the absorption of fatty acids and fat-soluble vitamins

Bile salts act as emulsifiers, breaking up fat into droplets, allowing lipases to digest them better 5.1.3 state source of one lipase – substate,

source and optimum pH

29

Bile is stored in the gall bladder until a hormone stimulates its release into the small intestines

http://www.foxriverwatch.com/liver_hepatic_damage_pcbs_1a.html

30

Small Intestine

Approx. 20 -25 feet long with villi and microvilli for a total surface area of 25 sq meters

3 areas:DuodenumJejunum Ileum

Most digestion occurs in the duodenumMost absorption occurs in the jejunum and ileum

31

The intestines are lined with villi Increase the surface area of the intestinal lining Increase the absorption of digestive productsCapillaries carry away absorbed products from villi

Nutrients are absorbed by several meansSimple diffusion (higher to lower concentration area)

Facilitated diffusion (Against the gradient using channel or carrier proteins)

Active transport (diffusion with ATP)

32

Microvilli on intestinal epithelial cells

33

As chyme enters duodenum it stimulates the release of pancreatic juices and mixes with enzymes from the pancreas and small intestine as well as with bile, fluid and bicarbonates

All the gastric, small intestinal secretions and pancreatic secretions are controlled by the nervous system and by hormones

34

Digestive enzymes in sm. intestine

Enzymes are specific to a particular substrate

ProteinsPeptidases break peptides into amino acids

LipidsLipases break lipids into glycerol and fatty acids

35

Carbohydrate Digestion

Begins in mouth with salivary amylase

Halted by hydrochloric acid

Digestion mostly occurs in small intestine by pancreatic amylase

Passes through intestinal wall in monosaccharide form (ex: glucose)

36

They quickly move through the digestive system

Some carbohydrates cannot be digested by humans and are excreted

They provide short term energy

37

Protein DigestionBegins in stomach by proteolytic enzymes

Most of digestion takes place in the duodenum by pancreatic and intestinal enzymes: Protein hydrolysis

Final phase occurs in the “brush border” of the microvilli

Absorbed in the amino acid form

Allergic reactions can occur when intact proteins pass through intestinal wall

38

Proteins move through digestive system 2nd fastest after carbohydrates

Once protein is broken down into amino acids, these are reassembled into 1º,2º,3º and 4º proteins the body needs:Hemoglobin – blood proteinAlbumin – in plasma; aids in blood clottingFibrinogen – blood clotting agent

39

Lipid Digestion

Begins in stomach with gastric lipaseMajor digestion occurs in small intestineBile and action of stomach/small intestine

break down large globules into smaller pieces

Lipase breaks down particles into fatty acids.

Cholesterol and fat soluble vitamins follow similar process

Lipids move slowly through the digestive system

They are stored as long term storage in the form of adipose tissue

http://www.sunyniagara.cc.ny.us/val/adipose2.html

http://www.gen.umn.edu/courses/1135/lab/kidneylab/kidneylab.html

41

Vitamins, Minerals and Fluids

Absorbed in the intestineEight liters of fluid are passed back and

forth across the membrane of small intestine to keep nutrients in solution

Vitamins and water pass unchanged from small intestinal wall into the blood stream

Absorption of mineral occurs in stages in small intestine

42

Large Intestine

Includes:Ascending colon transverse colondescending colonsigmoid colonrectum

http://www.fruit-eze.com/education/colon/

Large intestine primarily absorbs water, electrolytes and some vitamins

Bacteria break down undigested materialFormation and absorption of vitamin KFormation and excretion of waste products

http://www.fujinon.com/product/medical/ed0114.htm

44

Little digestion now occurs as it is mostly completed by this time.

Large intestine are about 5 feet long

Mixing movement and peristalsis occur but are much slower here.

Peristalsis occurs only 2 to 3 times/day.

45

Contain E. Coli (good form not 0157) that break down remaining food and aid in the formation of vitamin KNewborns and vitamin K

The solid waste consists of dead bacteria, undigested fiber and other products of digestion.