Key Concepts on New Material for Final Exam (Godoy Only) Flashcards
Where are proteins denatured and hydrolyzed, respectively? Where does final digestion and absorption occur?
Denatured in the stomach and partially hydrolyzed (by Pepsin)
Final digestion and absorption is in the small intestine
What type of transport do di- and tri- peptides use to get into the bloodstream?
Tertiary Active Transport
List some peptides of physiological relevance
Oxytocin, ADH, Bradykinin, Angiotensin II
List some polypeptides of physiological relevance
Gastrin, CCK, Glucagon, ANP
How are lipids found within the body?
Either compartmentalized (membranes) or bound to plasma proteins - because they are hydrophobic
Lipids are amphiphatic. What does this mean?
That they have both a hydrophobic and a hydrophilic part.
What is emulsification, where does it occur and what emulsifies fat droplets?
Bile acids emulsify fat droplets.
Occurs in the duodenum.
Aims to increase the SA of the hydrophobic lipid droplets. Important for lipase function.
Describe the process of degradation and absorption of lipids
Large fat drop (LCFA) broken down by bile salts to small emulsified fat drops (Triglycerides). Pancreatic enzymes (lipase, colipase) act on these and the degradation products (Monoglycerides and FFAs) are absorbed by micelles. Micelles can be absorbed.
SCFA can be directly absorbed.
What happens to the Monoglycerides and FFAs once they are absorbed?
LCFA –> ER for Re-esterification
Monoglyceride + FFA –> Triglyceride
Triglyerides go into Chylomicrons –> Exocytosis into lymphatic vessels –> thoracic duct –> vein
What happens to short/medium chain fatty acids once they are absorbed?
Don’t go into a chylomicron.
They are directly released into portal circulation. Bind to albumin
Describe some of the regulatory hormones of lipid digestion.
CCK - stimulates bile acid secretion and pancreatic enzyme secretion (activated when lipids enter duodenum)
Secretin - stimulate bicarb secretion from pancreas
Describe the physiological relevance of fatty acids
Energy - oxidation of FFAs bound to albumin in tissues
Structural - plasma membranes
Hormone Precursors - Prostaglandins
Energy Reserve - TAG in adipose tissue
Where does the synthesis of fatty acids occur? What are the substrates? How are they stored?
Occurs in the cytosol of the liver, mammary glands, adipose tissue cells.
Substrates = carbs or proteins consumed in excess
Stored as mono-, di-, or tri-glycerides –> in adipocytes (as lipid droplets), some in liver
What is needed in order for fat to be released from their TAG storage form?
Hormone Sensitive Lipase
Hydrolyzes the TAG, Mobilizes the fat
Where does Beta-Oxidation of fatty acids occur?
Mitochondria
What does Beta-Oxidation produce?
Acetyl CoA, NADH, FADH2, Net 129 ATP!
Where is reabsorption of water and Sodium highest in the GI tract? How much is absorbed in each part of GI? How is Na+ absorbed?
Jejunum > Ileum > Colon
More proximal GI absorbs more water.
55% of water absorbed in duodenum and jejunum, 30% in ileum, 14% in large intestine
Na mainly paracellular
How is calcium reabsorbed in the GI tract?
Apical Ca2+ channels
Ca2+-ATPase
All increased by Calcitriol
What is needed for Vitamin B12 reabsorption?
Intrinsic Factor
How are vitamins absorbed in small intestine?
Using a carrier or with a Na Cotransporter
How is iron absorbed?
Must be Fe2+
If Fe3+ –> needs Ferrireductase
Fe2+ is co-transported with H+ via Ferriportin
Iron that is in the heme group of Myoglobin, Hemoglobin can be taken up directly.
How is iron stored? How is iron mobilized?
Stored as Ferritin
Fe2+ into blood –> converted to Fe3+ –> combines with Apotransferrin to make Transferrin –> mobilizes iron - iron can go to tissues
Cells of Gi smooth muscle form a syncytium.
Yep.
What are systems that are located within the wall of the GI tract (intrinsic systems) controlled by?
Nerves = Enteric Nervous System
Endocrine Secretions: Secretin, Gastrin, CCK, GIP, Motilin
What are systems that are located outside the wall of the GI tract (extrinsic systems) controlled by?
Nerves - Vagus and Splanchnic
Endocrine Secretions = Aldosterone
Describe the 3 types of GI tract neurons
Dogiel Type I - small cell body, short dendrites, MOTOR neurons
Dogiel Type II - large cell body, 1-2 long dendrites, SENSORY neurons
Dogiel Type III - multiple shapes and functions
What are the neurotransmitters released by enteric neurons?
Conventional Transmitters: Norepinephrine, Epinephrine
Non-Noradrenergic, Non-Cholenergic (NANC): NO (inhibitory, reduces motility), VIP (Inhibitory, relaxation of smooth m., vasodilation), Substance P (Excitatory, increases secretion, motility)
Describe the SNS and PSNS GI Tract innervation
PSNS: ACh –> Stimulatory –> Increases secretion, Stimulates salivation
SNS: NA –> Inhibits ACh
Describe the slow waves (electrical impulses) of GI smooth muscle.
Continuous, slow waves in muscle fibers –> Causes GI rhythmic contractions (3-12/min)
Caused by Interstitial Cells of Cajal (ICC) – electrical pacemakers of smooth m. cells
NOT APs
Describe the spike potentials of GI smooth muscle electrical impulses.
These are Action Potentials
Occur when membrane potential reaches threshold (-40mV)
1-10 spikes/sec
What are the 3 main types of reflexes essential to GI control
- Reflexes integrated entirely within the gut wall (secretion, peristalsis, mixing)
- Reflexes from gut to sympathetic ganglia to GI (gastrocolic reflex, enterogastric reflex, colonoileal refle)
- Reflexes from gut to spinal cord/brain steam to GI (pain, defecation reflexes, gastric motor)
What is the Gastrocolic Reflex, Enterogastric Reflex, Colonoileal Relfex
Gastrocolic - signal from stomach - evacuation of colon
Enterogastric - signal from colon and SI - inhibit stomach motility and secretion
Colonoileal - signal from colon to inhibit emptying of ileal contents into colon
Describe the peristaltic reflex
Stretch of intestinal wall stimulates afferent neurons:
proximal to distention - excitatory neurons stimulated –> smooth muscles contract
distal to distention - inhibitory neurons stimulated –> smooth muscle relaxes
Describe the vagovagal reflex
Vagus nerve stimulated by mechanoreceptors in gastric mucosa - relaxes smooth m in stomach wall (also vagus n)
Describe the sequence of inflow from the gastric pump
- Tonic contractions in fundus (gastric store)
- Strong peristaltic wave in antrum (grinder)
- Passage into the grinder and then into the pylorus
- Emptying of fluid and digested particles into duodenum
What are the 2 phases of motility of the small intestine? What happens in each?
Digestive Period - propulsive pattern (persitaltic wave) and non-propulsive pattern (segmentation) Interdigestive period (Migrating Motoric Complex)
Describe the motility of the large intestine
Mixing of the large intestine
Peristaltic and Anti-peristaltic waves –> low propulsion
What are giant contractions? What is the consequence of oral vs aboral giant contractions?
High amplitude and long lasting contractions
Oral - vomiting
Aboral - diarrhea
Describe the sequence of events in vomiting.
1) Antiperistaltic wave originates in duodenum
2) Propulsion of ingesta towards stomah
3) Contraction of abdominal musculature increasing the intra-abdominal pressure
4) Expansion of chest cavity which glottis remains closed to LOWER to the intra-thoracic pressure
5) Relaxation of the lower esophageal sphincter.
6) Opening of the upper esophageal sphincter.
What are the 2 types of diarrhea?
Malabsorptive and Secretory
What is malabsorptive diarrhea and what can cause it?
Occurs when absorption is inadequate to recover all secreted water.
Destruction of villi and/or reduced length (rate of cell loss > replacement)
What is secretory diarrhea?
Occurs when rate of secretion > absorptive capacity
Describe the PSNS and SNS innervation of internal anal sphincter
SNS - contraction, PSNS - relaxation
What is the retrosphincteric reflex?
Afferent impulses stiulated by movement of feces into rectum –> PSNS efferent (pelvic n) Stimualtes peristaltic contractions of rectum and relaxation of internal anal sphincter –> Voluntary signals (pudendal n) control external anal sphincter (skeletal m)
What is the largest compartment of ruminant stomachs in newborns? Why?
The abomasum. Because does not yet have right microflora in order to ruminate.
What are the main 3 Volatile Fatty Acids? where do they go?
Propionic Acid (--> liver (glucose)), Acetic Acid (--> All tissues (energy)), Butyric Acid (Adipose tissue (fatty acids)) (Propionate, Acetate, Butyrate)
Explain how carbohydrates are broken down by the ruminant.
Polysacchardes (Cellulose, Hemicellulose, pectin) are hydrolyzed by Cellulase.
Monosaccarides (glucose) are NOT available for absorption by the animal. They are metabolized by the MICROBES.
In microbial cells glucose enter glycolytic pathway –> produces 2 pyruvate, 2 NADH, 2 ATP which is used by microbe.
Fermentative digestion is anaerobic and products are VFAs and SCFAs
Describe how acetate, butyrate, propionate and propionate & acetate are produced in rumen.
Glucose –> pyruvate –> Acetyl CoA –> Acetate
Glucose –> pyruvate –> Acetyl CoA –> Butyrate
Glucose –> pyruvate –> Propionate
Glucose –> pyruvate –> lactate –> Propionate & Acetate
What are proteins broken down to and by in the rumen?
Microbes produce endopeptidases. Break down proteins into peptides. Peptides are hydrolyzed by amino acids intracellularly. which can then go to microbial proteins or metabolized for production of energy (VFAs and ammonia)
Usually the Carbon structure of amino acids can be used for VFA synthesis. Except for…?
Branch Chain Amino Acids
Valine
Leucine
Isoleucine
what are the 2 sources of urea in the ruminant?
- From deamination of endogenous amino acids
2. Nitrogen absorbed as ammonia from rumen
How is urea recycled in the ruminant?
Portion of the urea that is excreted into the rumen can be resynthesized into protein that will contribue to the amino acid needs of the hosts (under low dietoary protein conditions, etc)
How do ruminants digest fat/lipids?
Micro-organisms have lipases, phospholipases.
Results in VFAs
Absorbed in small intestine and abomasum
Triglycerides, Glycolipids, phospholipids and free fatty acids are the main fats found in which types of food, respectively.
Triglycerides = cereal grain, oilseeds, animal fats, byproduct feeds, milk fat Glycolipids = forages Phospholipids = minor component of most feeds FFAs = minor component in dairy feeds, major component in some dietary supplements
What is the typical rumina ratio of acetic:propionic:butyric acid in animals with high forage diets vs. high grain diest
70: 20:10 - high forage
60: 30:10 - high grain
Which vitamins do microbes synthesize in the ruminant?
Vitamin C
Vitamin K
Vitamin B
Describe the [ ] of SCFA, Na, Cl, Mg, Ca, H2PO4, HCO3 and glucose in rumen
SCFA = 100mM Na = 20-110mM cl = 10-20mM Ca, Mg = 1-10mM H2PO4 = 10-15mM HCO3 = 20-60mM Glucose = <1mM
How are VFAs absorbed in the rumen epithelium.
- Ionized VFAs - these cannot diffuse and need a carrier (HCO3-/Ac- Antiport)
- Non-ionized VFAs - these are lipophilic and just diffuse across the apical membrane
What causes rumen acidosis?
Fast fermentable carbohydrates (starch rich diet) lead to increase in VFA production –> pH in rumen goes down
At a pH of <4.8 more VFA will be non-ionized and able to diffuse across the membrane into the cell
What does an acidic pH in the rumen stimulate in regards to bacteria?
Proliferation of lactate-producing bacteria –> exacerbates the acidosis
How is Na absorbed in the rumen?
Na channel
Na/H exchanger
Basolateral Na/K ATPase
How is Cl absorbed in the rumen?
Cl/HCO3 exchanger
Basolateral channel
How is K absorbed in the rumen?
Apical and basolateral channels
high luminal K+ [ ] –> transepithelial potential difference
How is Mg absorbed in the rumen?
Mg channel - dependent on potential difference between apical/basolateral sides
–> effected in presence of high K concentration (young pastures of potassium fertilized pastures) –> Pastures grass tetany
Travels opposite of K
What are the main functions of the omasum?
Concentration of ingesta (absorption of water)
SCFA (VFA) absorption (diffusion)
Na and Cl absorption
HCO3 absorption
What are the 2 kinds of motility patters in the rumen?
- Primary Contractions - Mixing
2. Secondary Contractions - Eructation
Describe the steps of primary contractions in the rumen.
- Bolus enters rumen, stays suspended by cardia
- Biphasic contraction of RETICULUM (1st contraction = weak, 2nd contraction = forceful –> bigger particles pushed to dorsal sac)
- Caudal moving contraction of dorsal sac moves ingesta further into dorsal sac
- Cranial moving contraction of dorsal sac mixes (bacterial fermentation occurs, produces gas, gas accumulates in dorsal sac)
- Smaller particles move to ventral sac
- Contraction of ventral sac separates particles into small and big –> smaller parts move over cranial pillar into cranial sac.
- Contraction of cranial sac –> further separation into big and small
- Reticulum contracts, reticulo-omasal orifice relaxes and small particles (dense material) are forced through opening into omasum (Big particles remain in rumen and mix again in dorsal sac)
Describe the steps of secondary contractions in the rumen. When do they occur?
Occur at end of primary contraction cycle.
- Cranial moving contraction starting in caudo-dorsal blind sac
- Forward moving contraction of dorsal sac that moves gas toward the cardia –> gas will enter esophagus and can be eructated.
Do reticulo-rumen contractions occur during sleep?
No.
About 1-3 per minute when awake, more when eating
What are the main gases produced in the rumen?
CO2 (60-70%)
Methane (CH4) (30-40%)
What is tympanism?
Bloating
Occurs when eructation mechanism fails
Where is the eructation center in the brain? What stimulates it?
In Medulla
Receives afferent impulses from mechanoreceptors in dorsal sac of rumen (Where gas accumulates)
What is legume bloat?
When cattle feed on lush, rapidly growing alfalfa or clover. Gas becomes trapped in tiny bubbles and the normal free gas bubble can’t accumulate in dorsal sac of rumen. Gas not detected by mechanoreceptors and eructation not triggeredd –> bloat.
Do horses have a mechanism to recover and utilize microbial proteins?
No. Pass out in feces.
Most carbohydrate digestion in ruminants occurs in he forestomach through fermentative digestion. Almost NO digestible carbohydrates enter in the intestine. Ruminants are in a constant start of potential glucose deficiency.So how do ruminants get glucose?
Gluconeogenesis. 85-100% of glucose needs.
Most important precursor for gluconeogenesis is the VFA Propionate!!
Propionate enters Krebs cycle as Succinate to produce Glucose.
Almost all propionate produced is extracted from the portal blood by the liver and never enters systemic circulation .
