Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

GI (Semester 4) > 7.1 The Intestines > Flashcards

7.1 The Intestines Flashcards

1
Q

What is the final product of the cephalic and gastric phase? What is this?

A

Chyme ➞ partially digested proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the features of chyme as it is delivered to the duodenum?

When it arrives at the duodenum what are its features and why?

A

Hypertonic, acidic and only partially digested

Becomes isotonic, neutral solution by mixing with Pancreatic secretions, Bile and Juices from the Intestinal wall

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe the process of gastric emptying

A

1) A peristaltic contraction originates in the upper fundas and swept down towards the pyloric sphincter
2) The contraction becomes more vigorous as it reaches the thick muscles antrum
3) The strong antral peristaltic contraction propels the chyme forward
4) A small portion of chyme is pushed through the partially opened spinchter into the duodenum (The stronger the antral contraction, the more chyme is emptied with each contractile wave)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe the process of gastric mixing (following gastric emptying)

A

1) When the peristaltic contraction reaches the pyloric sphincter, the sphincter is tightly closed and no further emptying takes place
2) When chyme that was being propelled forwards hits the closed sphincter, it is tossed back into the antrum. As chyme is propelled forwards and tossed back into antrum with each peristaltic contraction, mixing of chyme is accomplished

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What 2 things are required for optimal absorption to occur?

A

1) Large surface area

2) slow movement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

List 4 features of the intestinal lumen that increase SA

A

1) Plicae Circularis (transverse folds increase SA and decrease velocity of chyme)
2) Villi (epithelial covered finger-like protrusions with capillaries ending in a lacteal)
3) Microvilli ( modifications of apical plasmalemma of epithelial cells covering villi)
4) Crypts of Lieberkuhn (invaginations of epithelium into lamina propria forming intestinal glands)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Describe what happens to the Enterocytes in the Crypts of Lieberkuhn

A
  • Enterocytes multiple in the crypts
  • they migrate towards the tips of villi, maturing as they go
  • they acquire capacity to absorb
  • they are then shed from villus tips

(Mucosa is therefore constantly renewed)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are the 5 main cell types found in the crypts?

What do each secrete to contribute to intestinal juices?

A

Enterocytes: digestive enzymes
Goblet cell: mucus
Paneth cell: glycoproteins, immunoglobulin, lysozymes
Enterochromaffin cells: serotonin
Endocrine cell: GI hormones such as secretin, CCK, VIP, GIP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What do the cells found on the villi secrete? What happens to the products of these secretions?

A

Cells (enterocytes) villi secrete enzymes into brush border

This forms an ‘unstirred layer’
The enzymes secreted meet & react with enzymes secreted by enterocytes

End product is the steady release of small molecules for absorption

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the 2 places digestion occurs within the stomach

A

1) In the GI lumen by secreted enzymes

2) On surface of enterocytes by membrane-bound enzymes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the 5 main secretions that occur into the intestine to aid absorption?

A

1) Pancreatic exocrine secretions (pancreatic juices)
2) Bile from gallbladder (stimulated by CCK).
3) Intestinal Juice (brush border enzymes) that are “anchored” to apical surface
4) Mucous
5) Hormones: CCK, Secretin, GIP, GLP-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the function of bile secretion from the gallbladder?

A

Emulsifies the lipids, increasing surface area for pancreatic lipases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are 5 inactive zymogens hormones found in pancreatic exocrine secretions?

A 
Trypsinogen
Chymotrypsinogen
Procarboxypeptidase
Procolipase
Prophospholipase
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the main brush boarder enzymes?

A

Peptidases
Disaccharidases (maltase, sucrase, lactase)
Enteropeptidase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Where are the 2 places mucus that secreted into intestines come from and what is its function?

A

1) Brunner’s glands in the 1st few cm of the Duodenum, secrete large amounts of mucous that is alkaline to neutralise chyme
2) Goblet cells located along the length of intestinal epithelium and in the Crypts of Lieberkuhn also secrete mucus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

When the acidic chyme from stomach enters the small intestine, it stimulates cells in the intestinal lining to secrete 2 hormones.

What are these and what do they then go on to stimulate?

A

Secretin and CCK ➞ stimulate pancreas to secrete pancreatic juice and pancreatic enzymes

These pass through the pancreatic duct onto the ampulla of vater in the duodenum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the function of the following hormones (2 each):

Secretin
Cholecystokinin
Incretin hormones (GIP and GLP-1)

A

Secretin
• slows gastric emptying & gastric acid production
• Stimulates bicarbonate (HCO3-) production from pancreas to buffer acidic chyme

Cholecystokinin (CCK)
• secreted in response to lipids and slows gastric motility and gastric acid secretion
• acts hormonally on the hypothalamus

Incretin hormones GIP and GLP-1 (gastric inhibitory peptide and glucagon-like peptide1)
• Slow gastric acid and emptying
• stimulate insulin release from pancreas

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are the 2 main components of pancreatic juices?

What is the function of each

A

1) Bicarbonate ions ➞ neutralises acidic chyme into alkaline solution
2) Enzymes (amylase, protease, lipase, nuclease)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Intestinal juices finish digestion started by the pancreatic juices.

What enzymes are in these secretions and what is their function?

A

Intestinal juice is secreted by the intestinal walls

1) enterokinase: activates trypsinogen to tryspsin
2) Eripsin (peptise): converts polypeptides to amino acids.

3) Maltase: Maltose to glucose.
4) Sucrase: sucrose into glucose and fructose.
5) Lactase: lactose into glucose and galactose.
6) Lipase: breaks down fats into fatty acids and glycerol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How do CCK and Secretin act as both feedback and feedforward control?

A

Feedback: to further control gastric emptying
Feedforward: to promote digestion, secretion, motility and absorption of nutrients

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Explain the hormonal mechanism of CCK and Secretin

A

1) Chyme entering duodenum causes enteroendocrine cells to release CCK and secretin
2) CCK and secretin enter blood stream
3) CCK induces secretion of enzyme-rich pancreatic juices. Secretin causes secretion of HCO3- pancreatic secretions
4) Biles salts (and to a lesser extent, secretin) are transported via bloodstream to stimulate liver to produce bile more rapidly
5) CCK travels in bloodstream and causes gallbladder to contract and hepatopancreatic spinchter to relax allowing bile to enter duodenum

22
Q

Explain the neural mechanism of gallbladder secretion (NOT CCK)

A

During the cephalic and gastric phases, the vagal nerve stimulates the gallbladder to contract weakly

23
Q

During the intestinal phase, how are pancreatic zymogens activated?

A

1) Inactive zymogens in pancreatic secretions enter lumen of small intestine through pancreatic duct
2) Enterokinase in the brush boarder cleave trypsinogen into trypsin (from pancreatic juice)
3) trypsin then goes on to activate the following

Chymotrypsinogen ➞ chymotrypsin
Procarboxypeptidase ➞ carboxypeptidase
Procolipase ➞ colipase
Prophospholipase ➞ phospholipase

24
Q

Where does the MAJORITY of nutrient absorption take place?

What are the main exceptions

A

Jejunum

Exceptions:

  • Iron is absorbed in the duodenum
  • Bile salts, Vit B12, electrolytes and H20 are absorbed in the Ileum
25
Q

Starch (carbohydrate) is a mixture of what 2 compounds?

What are the bonds found in these?

A

Mixture of amyloses & amylopectin

  • Amylose – straight chains with 𝛼-1,4 bonds
  • Amylopectin – branched with 𝛼-1,6 bonds at branches
26
Q

What enzyme aids the digestion of carbohydrates, where does it come from and how does it act?

A

𝛼-amylases secreted in saliva and by pancreas act at 𝛼-1,4 bonds of amyloses to yield glucose (M) and maltose (D)

Acts to yield 𝛼- limit dextrins from amylopectins

27
Q

List the 4 main brush boarder enzymes and their function in the completion carbohydrate to glucose breakdown

A

Isomaltase: breaks down branched molecules at a-1,6 bonds
Maltase: maltose to glucose
Sucrase: sucrose to fructose and glucose
Lactase: lactose into glucose and galactose

28
Q

Explain the pumps involved in monoglycerides absorption?

A 
Monoglycerids = Glucose, Fructose, Galactose
Dissaccarides = Lactose

Glucose is absorbed actively using energy from sodium gradient (more Na+ = pump works harder). Glucose enters mucosal cells via 𝑁𝑎+/glucose transporter (SGLT1 which also transports galactose)

Glucose leaves cell to ECF by facilitated diffusion using the GLUT2 transporter

Fructose and lactose enter by facilitated diffusion NOT linked to 𝑁𝑎+

29
Q

In terms of glucose absorption, how can we treat Type II diabetes? (think transporters)

A

SGLT2 inhibitors

30
Q

Describe the basic principals of oral rehydration, what is contained in this fluid?

A
  • Uptake of 𝑁𝑎+ generates osmotic gradient so water follows
  • If we put Glucose in the Gut, the uptake will stimulate 𝑁𝑎+ uptake and generates an osmotic gradient of its own
  • So a mixture of glucose and salt will stimulate maximum water uptake

Oral rehydration fluid ➞ Sugar+ Salt+ Water

31
Q

How are amino acids digested and absorbed?

A

Digested:

Pepsin from chief cells in the stomach digests Proteins into oligopeptides
In the Duodenum it is peptidases from pancreas + Enzymes from Brush border from furthur digest these

Absorbed:

  • Most are ACTIVE, energy comes from Na+ transport
  • Some can come in by facilitated diffusion, then the active process kicks in when concentration equals.
  • some comes in from active transport of H+
32
Q

How are lipids digested and absorbed?

A

Digested

  • Bile salts emulsify fats
  • Pancreas lipases and colipases: break down fats in monoglycerides and fatty acids stored in micelles that enter the cell by diffusion

Absorbed:

  • digested products are combined with cholesterol and protein forming chylomicrons ➞ these are released in the lymphatic system
33
Q

How are water and electrolytes taken up?

A

Sodium taken up via diffusion into cell because of active transport across basolateral membrane

Chloride follows (due to the electrical gradient)

Osmotic gradient from all absorption leads to uptake of water

34
Q

How is Calcium taken up?

A

Only about 10% of ingested Calcium is taken up

Enters cell by facilitated diffusion (low [Ca2+]i)

Pumped out of basolateral membrane by 𝐶𝑎2+ ATPase (not very effective) so we need something else to help the absorption…

Vitamin D stimulated by PTH releases 𝐶𝑎2+from bone
and increases gut absorption of 𝐶𝑎2+

35
Q

Why is Iron important? (4)

How is it absorbed?

A

Iron is required for:

O2 transport (component of Hb)
DNA synthesis
Component of ribonucleotide reductase
As an electron acceptor/donor in the cytochromes

Absorption: (Fe2+ is difficult to absorb)

Gastric acid is important for Fe2+ absorption -> it solubilises iron complexes

These then move out of intestine where transferrin, carries the Fe2+ around the body

36
Q

What are the 2 types of Iron we have in our diet?

How do we absorb these are what are the 2 outcomes following absorption?

A

Ferric iron (Fe3+) and ferrous iron (Fe2+)

Fe3+ needs to be reduced to Fe2+ then absorbed by DMT-1 (co-transporter) into enterocyte

It is moved out of enterocyte by Ireg1 (ferroportin) and 2 things can happen:

1) it can be oxidised back to Fe3+ and stored as ferritin in the bone marrow, liver spleen and skeletal muscle
2) circulate in blood by transferrin (low amount)

37
Q

What are the 2 outcomes for the iron that is carried in circulation by transferrin?

A

75% Go to bone marrow for erythropoiesis

25% liver to be stored

38
Q

How do we absorb vitamins?

What is the exception?

A

Water soluble vitamins are absorbed largely by passive diffusion (C and B vitamins)

Vit B 12 can only be absorbed if it binds to Intrinsic factor, secreted by stomach mucosa (parietal cells-gastric pits) and only absorbed in the Terminal ileum

39
Q

What is the importance of Vitamin B12?

What is a deficiency in this called and how can it occur?

A

Important for synthetic processes ➞ specifically Hb

Vit𝐵12 deficiency = Pernicious anaemia

Can be caused by stomach damage or if the terminal ileum is removed

40
Q

List the 3 ways we SLOWLY move contents through the intestines?

How is transit time measured?

A

NOT PERISTALSIS!!!

1) Segmenting
2) Haustral shuttling
3) Mass movement (type of peristalsis)

Transit time measured in hours

41
Q

What is located at intervals along the small intestine that allow intestinal motility

How do these function and what process does this aid?

A

Intestinal pacemakers

Each pacemaker generates an AP which moves along plexus ➞ causes intermittent contraction of smooth muscle along length

Aids in segmentation

42
Q

What is the purpose of segmentation?

Describe the process

A

Purpose is to mixes and agitates food contents (NOT Propel them forwards)

The alternating contractions generated by the pacemakers creates segments along the intestines

Chyme is pushed back and fourth within adjacent segments of the intestine which mixes and agitates content

43
Q

How is food moved forwards if segmentation does not do this?

A

Although segmentation does not function to propel food forwards, an “intestinal gradient” is formed

This means that different segmentation rates in adjoining sections of the intestine cause a net movement of material in a caudal direction

The cephalic segment squirts more frequently AND faster than the caudal segment does (12 forward, only 11 backwards) results in food movement SLOWLY forward

44
Q

What is the purpose of the large intestine

A

Concentrating waste (through very slow motility and removal of water) to form a semi-solid material

45
Q

Describe the gastro-colic reflex and how is it related to defecation?

What are potential stimuli?

A

The gastrocolic reflex is a normal involuntary reflex that controls the motility/peristalsis of the GI tract following a meal

After eating there is an increase in motility of the colon in response to stretch of the stomach due to ingestion and byproducts of digestion entering the small intestine.

Thus ➞ this reflex is responsible for the urge to defecate following a meal.

CCK, serotonin and gastrin are potential initiators of this reflex

46
Q

What is meant by mass movement?

What triggers it?

A

Once or twice a day there is a peristaltic, propulsive pattern from the transverse through descending colon

This forces faeces rapidly into rectum (which is normally empty) which induces the urge to defecate

Often triggered by eating ➞ Gastro-colic reflex or by food in stomach

47
Q

What are the 3 things that occur to cause expulsion of faeces and what are the nervous stimuli?

A

1) Parasympathetic control via pelvic nerve: relaxes Internal smooth muscle sphincter
2) voluntary control of striated muscle via pudendal nerve (somatic): relaxes external sphincter
3) increase in Intra-abdominal pressure

Control via sacral reflexes modified by higher centres Higher centres overridden if rectal pressure too high

48
Q

What valve controls chyme entry into the colon and what stimulates it to?

A

Ileocecal valve controls chyme entrance into colon

It relaxes in sequence with intestinal peristalsis as well as when gastric emptying starts (gastro colic reflex)

49
Q

Explain the defection reflex

A

1) normally, the anal sphincters are closed by voluntary (somatic) and sympathetic stimulation
2) mass movement drives faces through the sigmoid colon and into the rectum ➞ rectum is distended
3) PNS afferent (sensory) fibres detect a full bowel (due to distention)
4) impulses are transmitted via afferent fibres of pelvic nerve to defecation centre
5) centre sends motor impulses via efferent fibres of pelvic nerve causing relaxation Internal smooth muscle sphincter
6) The cerebral cortex also send motor impulses via efferent fibres of the pudendal nerve causing voluntary relaxation of the external anal sphincter

50
Q

What are 2 characteristics of the large intestine

A

1) Haustra ➞ Colon divided naturally into segments known as haustra these are outpouchings of the intestinal wall
2) Taenia Coli ➞ 3 Longitudinal bands formed by the outer muscular layer of the colon

51
Q

Explain the process of Haustral shuttling

A

Contraction of smooth muscle in walls of haustra shuffles contents back and forth, the movement gradient is faster at start followed by gentle progression towards sigmoid colon

During this we get slow absorption of most remaining
water and salts, forming faeces

GI (Semester 4) (19 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions