ANSC 303 - TAMU - Exam 1

Passive Diffusion

--No transporter

--No energy required

--Moves with concentration gradient

Facilitated Diffusion

--Transporter

--No energy required

--Moves with concentration gradient

Active Transport

--Transporter

--Requires energy (ATP used)

--Can move against concentration gradient but doesn't have to

Pinocytosis

Cell surrounds and then pinches off vesicle

Enterocyte

Simple, columnar, intestinal absorptive cells that absorb most nutrients in the small intestine

SGLT1

Sodium, glucose linked transporter that cotransports glucose and Na+

-indirect active transport-

Sodium Potassium Pump

-Pumps 3 sodium out

-Pumps 2 potassium in

-Also referred to as ATPase

What must something do to "enter" the body?

Pass the lipid bilayer

T/F: The lumen of digestive tract is "outside" of body

True

Digestion occurs in a _________ environment

Liquid (H2O)

Salivary Amylase

Present in saliva that catalyses hydrolysis of starch (inactivated by low pH of stomach)

Lingual Lipase

Hydrolyzes medium/long-chain triglycerides into partial glycerides and free fatty acids

Cholecystokinin

CCK-controls motility of stomach and rate of passage

Folds of Ruggae

Allow stomach to expand

Examples of monogastric/non-ruminant species

Humans, pigs, dogs, cats, rats, mink

What about the stomach sterilizes its contents/killing all bacteria consumed in diet?

The acidic environment/low pH

What is responsible for low pH of stomach?

Secretion of HCl

pH of stomach

1-3

What hormone mediates stomach emptying?

Cholecytokinin (CCK)

4 Distinct Zones of Stomach

Esophageal

Cardiac

Gastric/Peptic (Fundus)

Pyloric

Pigs are susceptible to the development of ulcers where?

Esophageal region of the stomach

Kp

Rate of passage

-controlled by pyloric sphincter

Kd/Kd+Kp

Digestion--competitive process where Kd=rate of digestion

Digestive phisiology is closely limited to

1) food selection and dietary strategies

2) the ability of the animal to derive nutritional benefit from particular types of feed

Autoenzymatic

Digestive process carried out by enzymes of mammalian origin (monogastrics/non-ruminants)

Alloenzymatic

Extensive microbial digestion (ruminants)

Oral Cavity

Mechanical breakdown/mixing of food and saliva which decreases particle size

Saliva

Important for oral health and lubrication of food

Salivary Enzymes

Important for oral health/lubrication of food (amylase and lingual lipase)

Functions of Stomach

-storage

-digestion

-mixing/physical processing

-secretion

-absorbtion

Digestion

-Stomach-

The chemical acidity of 1-3 kills microbes, denatures proteins and activates pepsinogen

Secretions that protect stomach from acid

Buffer (HCO3-) and Mucus

Stomach Secretions

Acid (HCl)

Buffer

Enzymes

Mucus

Things the stomach absorbs

Water, Alcohol, Cu, F, Mo, Asprin

HCl Secretion

--Responsible for low pH in stomach

--Controls by nervous system and small intestine

T/F: The further down in the stomach you go, the more protected it is from acid

True

Gastroesophageal Sphincter

-Not true sphincter

-Too much relaxation=heartburn

-Separates esophagus and stomach

Pyloric Sphincter

--Separates pyloric region from duodenum

--regulates gastric emptying which is controlled to match the digestive capacity of the small intestine

Lipid in small intestine effect on gastric emptying and rate of passage

--Decreases emptying via CCK bc fat is difficult and slow to digest

--Decrease Kp=Increase extent of digestion

3 Types of Glands In Stomach

Cardiac

Oxyntic (peptic)

Pyloric

Cardiac Glands in Stomach

Produce mucus and buffer and protects cells

Oxyntic (peptic) glands in stomach

Produces acids and enzymes

Pyloric glands in stomach

Produce acid, enzymes, important for endocrine function

Esophageal region of stomach

-Contains squamous epithelial cells

-non-glandular

-most prone to heartburn

Cardiac region of stomach

Collumnar epithelial cells

Fundus region of stomach

Body, acid (product) and pepsinogen (secretion)

Pyloric region of stomach

Funnel/antrum

Hydrolysis

Change of a chemical bond accompanied by splitting of H2O

Small Intestine

Major site of digestion/absorption, secretion and immune function that is facilitated by great surface area and increased rate of passage

How do you increase time for enzymatic digestion and absorption?

Decrease rate of passage

Sphincter of Oddi

Controls flow of fluid from pancreas and gallbladder

Proximal Duodenum

"beginning"

-increases pH

-adds enzymes

-adds bile salts

Distal Duodenum

"end"

-absorbs CHO, AA, dipeptides and tripeptides

-LOTS absorptive structures

-LOTS structures to decrease rate of passage

Duodenum pH

5-6

Jejunum pH

7-7.5

Proximal Jejunum

LOTS enzyme production and nutrient absorption which decreases as food moves to distal jejunum

Jejunum absorbs what?

Carbohydrates, AA, dipeptides, tripeptides and lipids

Ileum pH

7.5-7.9

What does the Ileum absorb?

Bile and minerals

Ileum structure

-Few absorptive structures

-Few structures to decrease rate of passage

What supplies the small intestine?

Stomach, liver, pancreas, small intestine

What does the stomach supply to the small intestine?

Low pH digesta

What challenge does low pH digesta create for the small intestine?

Enzymes and enterocytes dislike low pH

What does the liver supply to the small intestine?

Bile to aid in lipid digestion

What does the pancreas supply to the small intestine?

Enzymes, buffer, electrolytes

What does the small intestine provide to itself?

Secretions that contain enzymes, buffer electrolytes

Kerkring Folds

Circular folds in mucosa and submucosa that are a permanent increase in surface area and decrease in rate of passage

Kerkring Folds are more dense/numerous/ closer together where?

Proximal regions

Villi

Line the small intestine to increase surface area

--each lined with enterocytes

Where are villi most dense/taller?

Distal duodenum, proximal jejunum

Where are villi shorter?

Distal jejunum

Central lacteal of villi

Lipid digestion

Vein of villi

Takes nutrients away

Artery of villi

Bring nutritents

Crypt of villi

Cell renewal/undifferentiated cells

How long does it take all enterocytes to get replaced?

8 days

Brush Border

Site of nutrient absorption

-top (lumenal) side of enterocyte

Microvilli

-lumenal surface of enterocyte

-site of nutrient absorbtion

-LOTS of transporters

-increases surface area

T/F: enzymes can be embedded in microvilli

True

Glycocalyx

Attached to microvilli

-serves as barrier that suspends food particles and enzymes which decreases Kp

What protects enterocytes from digestion?

Glycocalyx

Pancreas Functions

Exocrine and endocrine function

Exocrine Gland

Secretes outside of body, releases buffers, electrolytes, and enzymes into lumen of duodenum

Percent of pancreas that is exocrine

84%

Endocrine function of pancreas

Secretes inside of body, cells arranged into islets of langerhans

Alpha cells

Produce glucagon and increases blood glucose

Beta cells

Produces insulin and decreases blood glucose

Foregut alloenzymatic digestion

(+) microbial synthesis of AA

(-) easily digested nutrients are degraded/fermented by microbes

Hindgut alloenzymatic digestion

(+) the mammal digests easily digested nutrients

(-) do not benefit from microbial synthesis of AA and vitamins

Foregut fermentators

Microbial fermentation occurs in front of small intestine

--ruminents most complex

Hindgut fermentators

Microbial fermentation occurs after small intestine

--horses, pigs, cattle

Microbial Metabolism

Occurs via fermentation

-anaerobic

-fermentation converts sugars to acids, gasses and alcohol

Bacteria that play role in fermentation

Amylolytic, cellulolytic and proteolytic

Protazoa that play role in fermentation

Holotrichs, entodinomorphs

Fungi role in fermentation

Degrade structural components in plants

Pseudoruminants

-walk on pads

-3 compartment stomach (lack omasum)

-camels, llamas

Compartments of stomach

Reticulum

Rumen

Omasum

Abomasum

Reticulum

Honeycomb

Hardware

Get stuck in reticulum of ruminents and must be fixed by magnents

Omasum

"butcher's bible"

H2O absorbtion

Removable