Lecture Final: Chapter 20

Question 1

Animals need to satisfy three nutritional needs. What are they?

Answer 1

1. Chemical energy: Food intake → dietary carbohydrates → lipids → cytoplasmic pool of carbohydrates, fats → storage, building blocks, specialized derivatives, instant energy source
2. Organic building blocks: Food intake → dietary proteins, amino acids → ammonia → urea → urine or nitrogen-containing derivatives, building blocks
3. Essential nutrients / vitamins / minerals
   - - Cannot be synthesized; must instead be included in diet
   - - Essential fatty acids for mammals include Omega 3 and Omega 6
   - - Animals cannot store excess amino acids

Question 2

Digestive system pathway
+ parts (5)
+ segmentation and peristalsis, defined

Answer 2

Part of abdominal cavity

Pathway: mouth, esophagus, stomach, small intestine (with accessory glands and cecum), large intestine, rectum, anus

1. Mouth: ingestion point with chemical (hydrolytic enzymes) and mechanical (chewing) digestion
2. Esophagus: moves bolus (chewed food); extends through the diaphragm and into the stomach
   - - GI sphincter: allows entry of bolus from esophagus into stomach
3. Stomach: large pouch-like expansion of the gut that stores and mixes the food and also begins the digestion of proteins by secreting proteases that convert proteins into manageable polypeptides
4. Small intestine: divided into three smaller region on the basis of functions and internal differences (duodenum, jejunum, ileum) → three main functions
   - - Neutralize the HCl secreted by the stomach
   - - Digest the carbohydrates, proteins, and fats into smaller macromolecules
   - - Absorb these monosaccharides, amino acids, and small peptides and fatty acids and diacylglycerol along with other nutrients (ie vitamins), salts and water into the blood → simple sugars, amino acids, nucleotide breakdown products into capillaries + fats into lymph vessels
5. Large intestine: recovers water from unabsorbed foodstuffs, which are then processed into fecal matter; bacteria here help with chemical breakdown of refractory compounds and synthesize some vitamins

SEGMENTATION in small intestine, helps to disperse the fat in order to promote lipase chemical digestion – sloshing back and forth to counteract fats clumping together

PERISTALSIS throughout GI tract = involuntary waves of contraction and dilation in order to move food through the GI tract

Question 3

Helpers of the GI tract (4 ; 3sub2)

Answer 3

1. Mesenteries
2. Salivary glands
3. Accessory glands: inside small intestine; supply digestive enzymes, emulsifiers, and hormones that assist in digestion and absorption
   - - Liver: large and dark in color; detoxification, glycogen storage; also secretes bile (bile acids and pigments to help solubilize fat) and water, which are then stored in the gallbladder
   - - Pancreas: small and pinkish / grayish
   - —- Exocrine: digestive enzymes that hydrolyze proteins, carbohydrates, and fats and large quantities of bicarbonate ion HCO3- that neutralize the acidic chyme
   - —- Endocrine: glucagon and insulin; secreted into the blood to help regulate blood sugar levels
4. Cecum: located at junction of small intestine and large intestine; large diverticulum that stores bacteria that assist in enzymatic digestion of refractory carbohydrates (ie cellulose)

Question 4

Alimentary canal

• villi, defined
• four basic layers / tunics (3sub2)

(basically Histology of Duodenum, but new and improved)

Answer 4

Villi: folds that increase the surface area of the intestine

1. Mucosa innermost; three sublayers; form the lumen → function in absorption and secretion
2. Submucosa: areolar connective tissue; vascularized and innervated with lymphoid follicles and exocrine glands
3. Muscularis externa: inner layer of circular muscles and outer layer of longitudinal muscles
   - - SEGMENTATION in small intestine, helps to disperse the fat in order to promote lipase chemical digestion – sloshing back and forth to counteract fats clumping together
   - - PERISTALSIS throughout GI tract = waves of contraction and dilation in order to move food through the GI tract
4. Serosa: visceral peritoneum

Question 5

Saliva
+ functions
+ composition

Answer 5

mostly from submandibular / submaxillary glands

FUNCTIONS:

1. Keep mouth clean
2. Dissolve food chemicals for taste
3. Moistens food and compact into bolus
4. Production of amylase to start break down of starchy foods into shorter chains of sugars -
5. Production of lipase to start breaking down triglycerides

COMPOSITION:
Mostly Water / salt / mucus
+ Electrolytes
+ digestive enzymes (amylase and lipase)
+ proteins : mucin (compact into bolus), lysozyme (anti bacterial), IgA (Something), defensins (type of protein called cytokines, chemical signals for immune system)
+ some metabolic wastes (urea and uric acid – somehow)

Question 6

Deglutition

Answer 6

aka swallowing

Two major phases:

1. Buccal (voluntary) → push bolus into back of throat when tongue pushes against the hard palette
2. Pharyngeal-esophageal (involuntary) → controlled by swallowing center in brain stem
   - - Uvula elevates to block airway briefly; epiglottis also elevates to block windpipe
   - - Sphincter muscle will relax, allowing the bolus to enter the upper part of the esophagus

Question 7

Stomach
+ gastric glands
+ three phases of gastric secretion

+ autocrine and paracrine, defined

Answer 7

Typical four tunics of GI tract BUT two tunics (mucosa and muscularis) are modified

Gastric glands – modification of the mucosa → protect mucosa from the acidity of the stomach BUT low pH is necessary to activate a certain thing

• • Produce gastric juice → parietal cells secrete HCl and intrinsic factor (promotes absorption of vitamin B12 to help create RBC)
• • Chief cells secrete pepsinogen (inactive form of pepsin) and lipase
• • Enteroendocrine cells secrete a variety of chemical messengers
• —— Histimines: trigger inflammation
• —— Gastrin: hormone that stimulates production of HCl and pepsinogen

Autocrine: secrete something it acts on you
Paracrine: no duct; secrete something that acts on cells with appropriate receptors (usually neighbors)

Question 8

Three phases of gastric secretion

+ mechanism of HCl secretion

Answer 8

1. Cephalic phase → Parasympathetic stimulation of gastric stimulation → anticipation of eating
   - - Contrast to Sympathetic: fight or flight; digest later if you live
2. Gastric phase: distension / stretch receptors send message to the brain in order to release more gastrin
   - - Peptides can act as a buffer to an increase in acidity → helps to accelerate gastric production to continue digestion
3. Intestinal phase: initially enhances gastric secretion with chyme which stimulates enteroendocrine cells to release secretin and cholecystokinin (which primarily stimulate the pancreas and gallbladder) BUT will eventually inhibit gastrin secretion via hormone stomatasin

Mechanism of HCl secretion:
H+ (protons) actively pumped into stomach lumen by H-K ATPase antiporter, while HCO3- is exported into blood
– K+ can freely diffuse back out though

Question 9

How are things broken down?

• Carbohydrates
• Proteins
• Fatty acids

Answer 9

Carbohydrates are broken down into monosaccharides – move through microvilli and cells via secondary active transport, then into internal environment via diffusion

Proteins are broken down into amino acids – require secondary active transport to move into cell and across the brush order cells – diffusion into internal

Fat globules (triglycerides) are broken down by bile salts (antipathic, therefore part water soluble and part water insoluble -- ie soap) into emulsification droplets 
> droplets worked on by lipases (triglycerides into monoglycerides) to create monogly bile salts and free fatty acids
>> micelles will be formed and dispersed and can fall IN BTWN microvilli and diffuse right through into the cell bc nonpolar
>>> once inside, monogly and fatty acids combine to reform triglycerides, which are packaged into chylomicron
>>>> Chylomicrons exit cell by EXOCYTOSIS and enter the lymphatic vessels (as opposed to capillaries, which are too small)

Question 10

Throwback to GLUT2 Transport

Answer 10

Lumen – apical surface – epithelial cell – basal surface – blood stream

1. Na+ gradient established by Na/K ATpase – sodium will be high outside versus inside
2. SGLT1 (sodium glucose transporter 1) imports glucose into cell against concentration gradient by coupling it to the facilitated diffusion of NA – symporter bc sodium will move with gradient and into the cell; glucose will tag along (As sodium diffuses downstream its gradient, glucose will diffuse upstream its gradient)
3. Glucose allowed to diffuse passively into bloodstream into GLUT2.
4. When glucose is high in SI lumen, then the GLUT2 transporter will be inserted into APICAL membrane
   Amino acids also enter brush border cells by co transport with Na+

Question 11

Liver

• portal system
• functions (7)

Answer 11

“Portal system”: blood enters a capillary > moves into second capillary bed in the LIVER > then returns to the heart

1. Conversion of glucose into glycogen then stores
2. Synthesize blood proteins – helps to maintain osmotic pressure
3. Detoxification of natural and synthetic substances
4. Breaks down saturated fats and produces cholesterol
5. Bile salts and pigments, which are then stored in the gallbladder
6. Store fat soluble vitamins
7. Stellate macrophages removes debris and worn out blood cells from the blood as it flows past

Question 12

Large intestine

• microbiome
• functions (4)

Answer 12

Microbiome: has thousands of types of bacteria; ferment carbohydrates into short chain fatty acids; also produces B complex vitamins and vitamin K

1. Columnar epithelia without villi will absorb most of remaining water from indigestible food residues
2. Appendix contains lymphoid tissue and stores bacteria to recolonize gut when needed
3. mucosa is thicker with abundant goblet cells that produce mucus to ease passage of feces
4. Store residues temporarily and then eliminate from the body as semi solid feces

Question 13

Hormonal control of digestion

• PART 1: GASTRIC STIMULATION
• PART 2: CCK AND SECRETIN STIMULATION
• PART 3: CCK AND SECRETIN INHIBITION

Answer 13

PART 1: GASTRIC STIMULATION

1. Gastrin secretion by G cells in the stomach are stimulated by distention of stomach and increase of pH
2. Gastrin enters blood stream and circulates back to chief cells and parietal cells in gastric pits to stimulate secretion of pepsinogen and HCL, respectively. Also stimulates PERISTALSIS
3. Lowered pH of gastric juice inhibits further secretion of gastrin (negative feedback) in intestinal phase.

PART 2: CCK AND SECRETIN STIMULATION
Movement of chyme (from stomach) into SI stimulates release of secretin and cholecytoskin (CCK) from enteroendocrine cells In duodenal mucosal epithelium

— WHY ?? Chyme with high fat content provides strong stimulus for release of CCK; low pH chyme stimulates release of secretin.

• – WHAT DO THEY DO?
  
  1. CCK stimulates pancreatic secretions and gall bladder contractions
  2. Secretin stimulates release of HCO3-

PART 3: CCK AND SECRETIN INHIBITION
CCK and secretin inhibit gastric secretions and gastric motility, meaning that fatty meals have a longer residence time in the stomach.

Also, short nerve reflexes via enteric nerves and long reflexes via vagus nerve and sympathetic stimulation will inhibit gastric juice secretion

Question 14

Appetite regulating hormones (4)

Answer 14

Hypothalamus: central control for feeding

Leptin: produced by adipose tissue; suppresses appetite – when body fat decreases, leptin fall and then appetite
** Feedback loop

After a meal, SI secretes the hormone PYY which acts to counter the appetite stimulate ghrelin
– Btwn meals, stomach wall will secrete the hormone ghrelin that stimulates appetite

Also after a meal, Islets of Langerhans secrete insulin into the bloodstream – can lower blood sugar AND suppress appetite

Question 15

Dentition and Diet (5)

Answer 15

Mammals w heterodont dentition – heterodonty requires precise occlusion → carnivores in the front, omnivores in the back
– Different animals will have different dentition that best fits their diet

Enamel is hardest substance in the body bc 96% hydroxyapatite crystals
– Usually the oldest fossils you find

Dentin (70% hydroxypatite) supports enamel

Cementum: calcified and covers the root of the tooth

Dental pulp: living connective tissue; source of a toothache

Question 16

Ruminant Digestion

Answer 16

Ruminant = foregut fermenters
Stomach w four chambers

Consider the pathway of food in cows.

1. Food enters rumen and reticulum (non acidic vat containing anaerobic bacteria for fermentation)
2. Bacteria will digest cellulose, synthesize B vitamins, essential AA, and recover waste nitrogens
3. Cow regurgitates and rechew the cud – swallows again
4. Cud enters omasum where ions and waters are absorbed
5. Cud passes to abomasum (functionally equivalent to our stomach) – acidified chamber for digestion by cow’s own enzymes
6. Digested products are absorbed as material passes into intestine → Foregut fermenters digest microbes in abomasum and absorb in SI, which is posterior to abomasum

Question 17

Hindgut fermenters

Fecal matter differences btwn foregut and hindgut fermenters

Answer 17

Microbes are also full of vitamins BUT they are unavailable to hindgut fermenters bc beyond the location of pathway that allows for absorption (Located in cecum or colon of animals for downstream absorption)
– Contrast to foregut, which is early enough to allow for absorption

Therefore, to get these nutrients, hindgut fermenters will eat their fecal matter

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