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PSL 310 > Digestive Physiology > Flashcards

Digestive Physiology Flashcards

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1
Q

What is the function of the digestive system

A

To transfer nutrients (including water, salts or ions, and vitamins) to ECF (the internal environment)

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2
Q

Organs of the tract

A

Mouth, pharynx, esophagus, stomach, small intestine, large intestine

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3
Q

Accessory digestive organs

A

Salivary glands, liver, gall bladder, and pancreas

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4
Q

What absorbable units are carbohydrates, proteins, and fats broken down to

A

Carbohydrates-monosaccharides (mostly glucose, also galactose, and fructose)

Proteins-amino acids

Fats(triglycerides)-one molecule is broken down to 1 mono glycerine and 2 fatty acids

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5
Q

What enzymes are involved in digesting carbs, proteins, and fats

A

The enzymes that catalyze above reactions cause hydrolysis (add H20 at bond; breaks subunits)

Enzymes are biological catalysts specific for certain reactions

Main enzymes
Carbohydrate-amylase
Protein-pepsin
Fat-lipase

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6
Q

What are the 4 layers of the GI tract

A

Serosa-the outer layers of organ; it’s a membrane that secretes fluid. A layer covers the abdominal organs and is called the serosa aka visceral peritoneum.

Another layer of peritoneum lines the abdominal wall called parietal peritoneum

Muscle layer (muscularis externa)- it’s smooth muscle 
It has an outer longitudinal layer (which can contract and shorten the tube) and an inner circular layer (which can contract and constrict the tube) causes mixing and propelling movements of tract

Submucosa- connective tissue nerve cells, blood and lymph vessels and glands

Mucosa- the innermost layer of mucous membrane= membrane that secretes mucus which lines the entire tract

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7
Q

What are the two nerve plexus more within GI tract and what makes it special

A

Submucous (submucosal) and myenteric plexus

make up the enteric (intestine) nervous system

GI tract has own local nervous system; no other organ system has this

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8
Q

Short reflexes

A

From receptor to nerve plexus to effector

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9
Q

Long reflexes

A

From receptor to CNS to ANS fibers to nerve plexus To effector cells

(Sight or smell of food can cause GI responses)

These reflexes are through a CNS effect on autonomic neurons that go to GI tract

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10
Q

What does saliva include in it?

A

Contains mucus (protein) which lubricates the food

Saliva contains enzyme amylase

Saliva contains lysozyme an antibacterial enzyme-kills some bacteria

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11
Q

How does swallowing occur?

A

Boris of food is pushed by tongue into the pharynx which stimulates pressure receptors and their afferents t. Euro s that go to the swallowing center in the medulla oblongata

  1. The soft palate and uvula close off the nasal cavity
  2. The trachea is closed off which keeps food out of respiratory tract
    - epiglottis (flap at the top of larynx) covers larynx
    - glottis=the laryngeal opening closes because the vocal cords or folds come together
    - respiration’s are inhibited
  3. The bolus passes the upper esophageal (or pharyngoesophageal) sphincter which then closes.

Steps 1-3 are known as oropharyngeal phase abs takes about 1 second

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12
Q

Esophageal phase

A

Primary Peristaltic wave moves the bolus of food into the stomach

If the primary peristaltic wave can’t get the bolus to stomach the distention of the esophagus triggers secondary peristaltic waves

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13
Q

Heart burn

A

Occurs when acidic gastric contents move into esophagus and irritates it.

Can occur with large meal and a full stomach or during pregnancy

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14
Q

How can pregnancy trigger heartburn

A

Enlarged uterus can push the lower esophageal sphincter up from abdominal cavity into thoracic cavity (where pressure is lower)

Increased abdominal pressure can force stomach contents into esophagus

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15
Q

What are the regions of the stomach

A

The stomach is located in the abdominal cavity

Regions=fungus (upper part, above the esophagus opening), body (middle part), antrum (lower part, with thick muscle)

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16
Q

Pyloric sphincter

A

Is at junction of the stomach and the first part of small intestine (duodenum); it is a sphincter of strong circular muscle

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17
Q

Chyme

A

A sludge (thick liquid); the stomach makes what’s been described as a smoothie which includes partly digested food solution, with enzymes too- salivary amylase and (will see soon) another enzyme is added

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18
Q

What are the functions af HCl?

A

Secreted by cells of the stomach called parietal cells

Functions: 
Kills microorganisms (remember lysozyme in saliva does too) -kills most microorganisms that enter food, but some make it to large intestine and divide there

Uncoils proteins- remember H+ affects protein shape; decreases food particle size by affecting connective tissue proteins

Activates pepsinogen

Creates an acid environment for pepsin (needs acid to work/be active

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19
Q

Pepsinogen

A

Secreted by chief cells

Pepsin (from pepsinogen) is a protein digesting enzyme (starts doesn’t finish breakdown)

Pepsin secreted in inactive forms (called pepsinogen) which protects the secreting cells from self digestion (a lot of cell structure is made of protein)

HCl helps activate pepsinogen- the low pH affects the enzyme shape allowing it to become active

Pepsin can then activate pepsinogen!

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20
Q

Where are the chief cells and parietal cells located

A

Are in gastric glands-are below gastric pits

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21
Q

Function of mucus secreted in stomach and through your tract

A

Forms protective coating

Is alkaline, has bicarbonate ion which helps neutralize acid next to stomach mucosa and protects stomach from damage

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22
Q

What secretes intrinsic factor

A

Parietal cells secrete it abs it’s needed for vitamin B12 absorption

Intrinsic factor is essential. Need B12 for DNA and hemoglobin synthesis therefore RBC production

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23
Q

Gastrin

A

a hormone
Different kind of secretion
Effects are not in stomachs lumen it goes into the blood to cause effects

Secreted by cells in Antrum of the stomach (inferior end)

Travels to other areas of the body through the blood including the body of the stomach

Stimulates acid secretion by parietal cells

Controls HCl secretion

Stimulates chief cells to secrete pepsinogen

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24
Q

Gastric emptying

A

Peristaltic waves are stronger in the antrum (thicker muscle) 

These waves mix the contents and close the pyloric sphincter

Before it closes the sphincter small amount of chyme moves into duodenum

Most chyme is forced backward

Mixing of chyme therefore happens mostly in Antrum where contractions are strongest

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25
Pacemaker cells
Create slow waves-oscillations in membrane potential which cause a basic electrical rhythm Won’t cause much contraction but if depolarizer further could increase strength of contraction Nerves and hormones can depolarize further- can prevent contraction or cause stronger constrictions
26
What factors in the stomach affect stomach emptying.
Increased fluidity will cause increased emptying Increased chyme in the stomach (increased distention, increased gastric motility, increased emptying) stronger contraction
27
What factors in the stomach affect stomach emptying
Increased distention of duodenum Increased fats, hypertonicity (or increased osmolarity), acid in duodenum-these all decrease stomach emptying
28
What is the enterogastric reflex
1. Stimulus in duodenum (distention, fats, hypertonicity, acid) 2. Activation of receptors 3. Afferents impulses to CNS 4. Efferent impulses (via ANS neurons) to the stomach, decreases stomach peristalsis and emptying (Long reflex) Can also occur via short reflex or within the tract reflex Stimuli in duodenum (increased fats, increased acid, increased osmolarity (or hypertonicity)) Receptor->enteric nervous system nerve plexus(es) -> stomach smooth muscle-decreases contraction
29
What hormones are released from small intestine to decrease antral contractions?
Hormones called enterogastrones are released. Fats, hypertonicity, acid, distention can cause the release of this hormone Pathway 1. Stimuli in duodenum (increased fats, increased acid, etc) 2. Small intestine endocrine cells release enterogastrones 3. Increased enterogastrones go into blood and travel to the stomach and decrease stomach emptying This is because the stomach needs time to churn and digest so it slows when a lot of food etc
30
Increased acid in duodenum
Bicarbonate from the pancreas normally neutralizes acid from the stomach-need to slow down emptying to neutralize what’s there (need to wait for more bicarbonate from the pancreas
31
Increased fat in duodenum
Fats take longer to digest and absorb than other foods- stop stomach emptying till can take care of fat that’s there
32
Increased hypertonicity
(increased osmolarity occurs when break one large molecule into many small molecules, for example, one protein molecule becomes hundreds of amino acids with digestion in small intestine) Water moves toward increased osmolarity would move from plasma and decrease volume so reduce amount entering the stomach decrease stomach emptying until absorption of food molecules can occur
33
Increased distention of duodenum
Slow down stomach emptying to give time to deal with what’s already there The intestine can tell the stomach to stop It’s how the stomach is emptied at a rate that is best for digestion plus absorption
34
What are released by small intestine to inhibit the stomachs activity
Enterogastrones (hormones) Including cholecystokinin (CCK), secretin, and others are released from duodenum to inhibit the stomachs activity- inhibit motility (movement) ALSO INHIBIT THE STOMACHS SECRETION
35
What is emptied into the small intestine
Gastric contents empty into it and exocrine (secrete through ducts) pancreas and liver add their secretions to the small intestines lumen
36
What does the pancreas secrete
Secreted enzymes and a bicarbonate solution-exocrine part Secreted hormones-endocrine part Enzymes are secreted by acinar cells Bicarbonate rich solution secreted by duct cells
37
Exocrine glands
Secrete into ducts
38
Endocrine glands
Secrete hormones into the blood
39
What are the pancreatic enzymes
Amylase Several protein digesting enzymes (secreted in inactive forms Lipase
40
Pancreatic amylase
Starch digested started by salivary amylase continues working in the stomach (in middle of mass of food) until mixed it’s with HCl (which inactivated it) Pancreatic amylase continues job. It digests carbs to disaccharides and alpha limit dectrins Still not done with digestion of carbs
41
Protein digesting enzymes
Secreted in inactive forms (like pepsinogen from the stomach, need to be activated outside the cell- in the linen of digestive organ to protect the secreting cells from self digestion Pancreas secreted trypsinogen- an inactive form of protein digesting enzyme Enterokinase (enteropeptidase) is an enzyme on cell membranes of mucosa cells of the duodenum Enterkinase splits a peptide off trypsinogen which forms trypsin trypsin actives other inactive enzymes then Also Chymotrypsinogen to chymotrypsin Procarboxypeptidase to carboxypeptidase
42
Which protein digesting enzyme splits bonds of proteins in interior
Trypsin and chymotrypsin
43
Which protein digesting enzyme splits bonds of proteins on carbonyl end
Carboxypeptidase
44
Pancreatic lipase
This enzyme breaks a fat molecule into absorbable units - mono glycerine and 2 fatty acids per one fat molecule Need bile (bile salts) for lipase to work well
45
Bicarbonate ion- in an alkaline solution
Secreted by the pancreas Neutralizes acidic chyme from stomach- protects the duodenum from stomach acid Also created a favorable pH for the enzymes to work (less acidic)
46
Regulation of pancreatic secretion
Controlled by two hormones 2 enterogastrones released from duodenum-secretin and cholecystokinin (CCK)
47
Secretin (released from duodenal mucosa)
Released in response to acid in the duodenum Causes the pancreas (duct cells) to increase release of bicarbonate rich/alkaline solution Neutralizes acid from the stomach
48
Cholecystokinin (CCK) (released from duodenal mucosa)
Released in response to fat (main stimulus) and protein products in the duodenum Causes the pancreas (acinar cells) to release an enzyme rich secretion which digests the food molecules more
49
Bile
Secreted from duodenum Made by the liver and stored and concentrated in the gallbladder Bile contains: bile pigments (bilirubin mostly, from hemoglobins heme), cholesterol, bile salts (derivatives of cholesterol IMPORTANT) and lecithin (a phospholipid
50
How do bile salts assist in fat digestion
They are NOT enzymes They act like detergent and keep fats broken up in small droplets (need them since fat isn’t water soluble and want to clump togeth)
51
What does it mean to emulsify fats
When break a large fat drop or glob into smaller droplets Emulsion greatly increased the surface area for pancreatic lipase to act Bile salts maintain the emulsion The charges on bile salts means that emulsion droplets repel each other
52
What is the other function of bile salts
Bile salts help in fat absorption by forming micelles Have inner core that is hydrophobic and outer surface that is hydrophilic Products of fat digestion can dissolve in hydrophobic core of the micelles/ “ride” in core Micelles transport products of fat digestion through water in lumen of small intestine to the mucosal lining of small intestine where they are absorbed
53
Stimulus of bile release
Secretion of bile by the liver is continual Between meals bile is pushed to the gallbladder; the opening to duodenum is closed During meal gallbladder contracts and empties into the duodenum Signal for gallbladder contraction is CCK CCK also causes relaxation of sphincter of oddi- around duct where it opens into the duodenum
54
After bile salts help with fat digestion and absorption what happens to them?
They are reabsorbed and returned to the liver and resecreted Enterohepatic circulation- The recycling path between intestine and liver via the hepatic portal vein
55
What is secreted into the lumen of small intestine
Pancreatic enzymes, bicarbonate solution, and bile
56
Why is the small intestine composed of villi and microvilli
This increases the surface area for absorption
57
Nutrients are absorbed into the capillaries except————-?
Fats. They are absorbed in lacteal of the villus
58
What happens after the nutrients are absorbed into the capillaries?
Blood from intestines does not go directly into vena cava First goes to liver for processing of nutrients via the hepatic portal vein Portal system = capillaries —-hepatic portal vein——capillaries again (liver sinusoids) Fats go into lymph system
59
Fats go into ——- system
Lymph
60
How does Na+ aid in absorption of nutrients
Many nutrients rely on active transport of Na+ Na+ is absorbed and substances are reabsorbed with Na+, then water lots follows For simple sugars, amino acids it’s secondary active transport. They get free ride in powered by Na+ gradient
61
Most absorption occurs in the _____
Small intestine Start carb in mouth, start protein in stomach, all the rest in small intestine
62
How is fat absorption different than other nutrients?
Absorbed into the lymph in small intestine (bile salts maintain lipid emulsion, pancreatic lipase hydrolyzes fats, are water insulator so carried by micelles to luminal mucosal surface of small intestine) Passive diffusion of fatty acids and monoglycerides from micelles through intestinal mucosal cell membrane -since are lipid soluble Once inside intestinal cell, fats are resynthesized then are packaged- fat molecules are enclosed or coated with lipoprotein (makes chylomicrons) Exocytosis of chylomicrons occurs Chyclomicrons cant enter blood capillary instead must go through lacteal/lymph vessel of villus
63
What are the fat soluble vitamins
A,D,E,K CARRIED IN MICELLES are absorbed with products of fat digestion
64
What are water soluble vitamins
B, C Use diffusion or carrier mediated transport to enter mucosal cells Exception is B12- needs to be bound with intrinsic factor (from the stomach) and is absorbed by endocytosis in the terminal ileum
65
Motility (movements) of small intestines
Need to mix chyme with secretions and expose chyme to the absorptive surface and after absorption need to move what’s left into the large intestine Segmentation Mixes chyme Also slowly propels chyme Divided into segments like sausages Mixed chyme with enzymes and exposed chyme to absorptive surface/ mucosa
66
Small intestine also has _____________like the stomach
Basic electrical rhythm (BER) Slow waves in small intestine that set the frequency for segmentation Frequency higher in duodenum versus ileum More activity above moves stuff down
67
Segmentation is affected by….
Gastric emptying- increased segmentation (with distention of duodenum) Gastroileal reflex- chyme in the stomach causes gastrin release which increases segmentation in the ileum Extrinsic nerves ANS- parasympathetic increases segmentation Sympathetic decreases segmentation
68
What occurs after segmentation and absorption?
MMC occurs (migrating motility complex) 3 phases- in phase 3 peristaltic waves begin in stomach and move (migrate) down to the end of the ileum (then this repeats) (stomach growling) Function- moves undigested material, also bacteria, into large intestine Thought to be controlled by the hormone motilin from small intestine
69
What is the function of the large intestine
No enzymes are secreted (so function is NOT digestion) Mucus is secreted A.) absorption of water and electrolytes from chyme B.) storage of fecal material- undigested material and bilirubin
70
Where is out bacterial flora located
The large intestine Living bacteria produce vitamins including vitamin K Vitamin K is needed for blood clotting Bacteria break down substances we can’t (like carbs in beans) produce gas (from their metabolism which is expelled out the anus- called Claris or flatulence
71
Haustral contractions
Mixing movements of large intestine Similar to segmentation but much less frequent Slowly mixed the contents when a sac then becomes a contracted part Also exposes what’s inside the inside to absorptive mucosa
72
Mass movements
Typically follow meal occurs with gastroileal reflex Gastrin also increases colons activity- gastrin initiated mass movements Distention of rectum with mass movement stimulates stretch receptors and leads to defecation reflex
73
Defecation is an ______________ reflex
Autonomic 1. Internal anal sphincter is smooth muscle (involuntary) Reflex causes it to relax External anal sphincter is skeletal muscle (voluntary) Can contract to delay defecation (Potty training is learning how to control external anal sphincter)
74
How long does food stay in stomach
Few hours depending on fluidity and fat content
75
How long does food stay in small intestine
3-5 hours
76
How long does food stay in large intestine
More than 10 hours maybe even 24 hours or longer
77
Where is most alcohol absorbed
Small amount of alcohol absorbed in stomach. Majority absorbed in small intestine.

PSL 310 (8 decks)

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