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gastrointestinal system Flashcards

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1
Q

what are the functions of GI secretions?

A
  • chemical digestion
  • lubrication -> mucus secretions, help movement of food
  • signalling
  • protection -> stomach acids
  • activation of enzymes
  • excretion of waste
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2
Q

exocrine glands

A
  • local action
  • produce and secrete substances onto an epithelial surface by way of a duct
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3
Q

endocrine glands

A
  • local or systematic (can be in the blood stream)
  • secrete their products, hormones directly into the blood rather than through a duct
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4
Q

gastric secretions

A
  • acid
  • pepsin
  • gastric lipase
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5
Q

liver / gallbladder

A
  • secretion, storage and modification of bile
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6
Q

salivary glands

A
  • lubricating fluid containing enzymes that break down carbohydrates
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7
Q

pancreas

A
  • exocrine cells: secrete buffers and digestive enzymes
  • endocrine cells: secrete hormones
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8
Q

small intestine

A
  • digestive enzymes
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9
Q

large intestine main role

A

reabsorption of water

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10
Q

types of salivary glands

A
  • major salivary glands
  • minor salivary glands
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11
Q

major salivary glands

A
  • 3 pairs
  • exocrine -> secrete saliva via a duct
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12
Q

minor salivary glands

A
  • 600-1000
  • mucosal lining of the oral cavity, lips, cheeks and palate
  • exocrine with own duct
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13
Q

what does saliva consist of?

A
  • 99.4% water
  • 0.6%: mucins, electrolytes, antibodies (immuniglobin), enzymes (amylase)
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14
Q

function of saliva

A
  • buffer -> ions keep pH at 7
  • mucosa stays moist
  • protects against any mechanical damage
  • needed for speech
  • solvent -> dissolves chemicals in food to help taste receptors detect them
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15
Q

what is xerostomia?

A
  • sensation of dryness in mouth due to prolem in saliva production
  • symptoms include: acid erosion of teth, infection, cracked lips..
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16
Q

how is saliva production controlled?

A

by the automic nervous system

  • both parasympathetic and sympathetic divisions
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17
Q

role of parasympathetic ns in saliva production

A

it controls the volume of fluid secreted
(cranial nerves 8 and 9)

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18
Q

role of sympathetic ns in saliva production

A

modulate the composition of saliva (e.g. amylase, IgA)
(somatic nerves 1-3?)

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19
Q

gastric secretions

A
  • stomach: exocrine and endocrine secretions
  • gastric juice helps stomach functions
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20
Q

what does gastric juice contain?

A
  • water
  • HCL
  • pepsinogen
  • intrinsic factor
  • mucus
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21
Q

why does the stomach have 2 sphinctors at each end?

A

to prevent things leaving & entering the worng end of stomach

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22
Q

what is heartburn?

A

when stomach acid goes back up into the oesophagus (acid reflux)

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23
Q

gastric gland cells

A
  • parietal cells
  • chieff cells
  • mucous cells
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24
Q

role of parietal cells?

A

secrete intrinsic factor

  • needed for vitamin B12 absorption
  • secrete HCL which kills microbes, denatures proteins and activates enzymes
  • in stomach
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25
Q

role of chief cells?

A

secrete pesinogen
- converted to pepsin in its active form
- breaks certain peptide bonds

secrete gastric lipase
- splits short-chain trigylcerides into fatty acids and monoglycerides
- the first enzyme that starts breaking down lipids in the stomach

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26
Q

at what pH is pepsinogen activated to pepsin?

A

low pH due to highly acidic environment in the stomach

(pepsinogen found in stomach)

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27
Q

role of mucous cells?

A

secrete mucous

  • forms a protective barrier
  • has alkaline properties

superficial epithelial
mucous neck cells

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28
Q

exocrine pancreatic secretions

A
  • water
  • bicarbonate
  • enzymes
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29
Q

pancreatic enzymes

A
  • amylase, lipases and nucleases: secreted in active form -> need ions / bile for optimum activity
  • proteases: secreted in inactive form -> activated in duodenum
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30
Q

why are proteases secreted in inactive form?

A

to prevent them from digesting the pancrease

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31
Q

endocrine pancreatic secretions

A

alpha cells:
- secrete glucagon in response to fall in blood glucose
- stimulates glycogenolysis and gluconeogenesis

beta cells:
- secrete insulin to respond to rising blood glucose
- inhibited by adrenaline in acute stress
- allows cells to utilise glucose

gamma cells:
- secrete somatostatin
- stmulated by cholinergic innervation
- inhibits gastrin release

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32
Q

bile

A
  • produced by hepatocytes
  • pH 7.6-8.6
  • 800-1000mL per day
  • excretory product
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33
Q

what does bile contain?

A
  • bile salts
  • bilirubin
  • cholesterol
  • neutral fats
  • phospholipids
  • electrolytes
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34
Q

bile functions

A
  • lipid assimilation
  • elimination
  • neutralise gastric acid and provide optimum pH for pancreatic enzymes
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35
Q

gallbladder

A
  • thin-walled, pear-shaped
  • muscular sac on the ventral surface of the liver
  • stores and concentrates bile by absorbing its water and ions
  • releases bile via the cystic duct, which flows into the bile duct
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36
Q

phases in secretion regulation

A
  • cephalic phase
  • gastric phase
  • intestinal phase
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37
Q

cephalic phase

A
  • smell, sight, thought and taste of food activates CNS
  • facial, glossopharyngeal and vagus nerves are activated
  • salivary and gastric glands activated
  • prepares mouth and stomach for food (moist mouth)
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38
Q

gastric phase

A
  • food distends the stomach and stimulates stretch receptors
  • chemoreceptors in stomach detect increase in pH
  • peristalsis and gastric juice secretion
  • chyme empties into duodenum
  • low pH and low distension
  • negative feedback loop
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39
Q

intestinal phase

A
  • starts when food enters small intestine
  • inihibits exit of chyme from stomach
  • contraction of pyloric sphincter to prevent things entering stomach or small inestine
  • promotes digestion of food in small intestine
  • neural enterogastric reflex
  • hormones: cholecystokinin and secretin
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40
Q

when are cholecystokinin and secretin hormones released?

A

during the intestinal phase of digestion

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41
Q

what effect do cholecystokinin and secretin have on gastric secretions?

A

inhibitory

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42
Q

absorption

A

when small molecules move through epithelial cells into underlying blood or lymphatic vessels
- in GI done to get nutrients back into the blood

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43
Q

where does the most absorption take place?

A

the small intestine

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44
Q

large intestine

A
  • receives undigested / unabsorbed material
  • has a large microbiota that can break down more food and nutrients to be able to be absorbed
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45
Q

how can absorption occur?

A
  • simple diffusion
  • facilitated diffusion (neded if charged)
  • active transport (primary or secondary / coupled)
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46
Q

secondary active transport

A
  • does not directly need energy
  • use a cotransporter
  • only let a molecule back in via diffusion that initially moved out of membrane via active transport if it couples with another molecule -> that other molecule indirectly uses active transport
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47
Q

job of absorption in GI tract?

A
  • key to intestinal absorption: Na+/K+ ATPase on the basolateral membrane
  • to build a Na+ gradient outside the cell so that Na+ will want to move back into the cell
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48
Q

what needs to be absorbed?

A
  • carbohydrates
  • lipids
  • proteins
  • nucleic acids
  • vitamins
  • minerals
  • water
  • drugs
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49
Q

carbohydrates

A

starch:
- polysaccharides that need to be broken down
- long chains of glucose units
- found in rice, pasta, potatoes..

sugars:
- shorter chains
- mono/disaccharides
-found in fruit, veg, diary…

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50
Q

in what form are carbohydrates absorbed?

A

as monosaccharides

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51
Q

lactose is broken down by enzyme lactase. what would happen if that enzyme is not present?

A

lactose will not be broken down
has an osmotic pull on water so water will not be absorbed -> diarrhea can occur

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52
Q

why do carbs need to be broken down to an absorbable size at brush border instead of in the small inestine lumen?

A

prevents bacteria in the lumen potentially using it as nutrients

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53
Q

which monsaccharides neeed energy for absorption?

A

-glucose
- galactose

54
Q

proteins

A
  • long amino acid chains -> polypeptides
  • meat, fish, diary, eggs, pulses, cererals
  • also absorbed from digestive juices and dead mucosal cells
55
Q

amino acid absorption

A

each amino acid has a different cohort of transporters

56
Q

examples of lipids

A
  • triglycerides
  • phospholipids
  • cholesterol
  • steriods
  • fat-soluble vitamins
57
Q

lipid absorption

A
  • lipases break trigylcerides into monoglycerides and fatty acids (long or short chain)
  • simple diffusion
58
Q

problem of lipids in the watery GI tract environment

A

causes lipids to clump together
to be absorbed they need to be in small amounts instead of clumps

59
Q

emulsification

A
  • breaks large lipid droplets into smaller droplets
    -> increases surface area
  • starts in stomach with churning
    -> allows enzymes to break them down into even smaller parts
  • bile salts: have hydrophobic and hydrophilic regions
60
Q

chylomicrons

A
  • formed when lipids recombine in sER in SI epithelial cells
  • proteins are added
    -enter lymph instead of blood because they are too big to enter the blood wall & dont interact well with blood components
61
Q

vitamins

A

organic substances that cant be made by the body

62
Q

vitamin absoprtion in the small intestine

A

fat soluble:
- vitamins A,D, E and K
- carried by micelles -> then diffuse into absorptive cells

water soluble:
- vitamins C and B
- absorbed by passive or active transporters

vitamin B12:
- binds with intrinsic factors
- absorbed by endocytosis

63
Q

vitamin absorption in large intestine

A
  • vitamins K
  • B vitamins from bacterial metabolism
64
Q

how could a blockage of the bile duct lead to vitamin E deficiency?

A
  • it is a fat soluble vitamin
  • needs to be emulsified in the bile duct
  • needs to be carried with a micelle
    -> bile duct needed for formation of this
65
Q

electrolyte absorption

A
  • along lenth of small intestine
  • active transport
  • iron: enters via divalent metal ion transporter 1
  • calcium: absorption regulated by vit D and PTH
  • Na+: coupled with absorption of glucose and amino acids
  • K+: diffuses due to osmotic gradients
66
Q

water absorption

A
  • around 9L absorbed per day (many are recycled secretions -> absorb water frpm that)
  • 95% in small intestine by osmosis (osmotic gradient)
  • disturbance in this mechanism = water loss
  • net osmosis occurs when the concentration gradient is established by active transport of solutes
  • water uptake coupled with solute uptake
  • paracellular = between cells (with osmotic gradienr)
  • well regulated in tight junctions (controls which substances water is coupled with)
67
Q

causes of malabsorption

A
  • interferences with delivery of bile or pancreatic juice
  • damaged intestinal mucosa
  • gluten-sensitive enteropathy (celiac)
    -> gluten damages the intestinal villi and brush border
68
Q

functions of the liver

A
  • metabolism
  • detoxification
  • excretion
  • storage
  • synthesis
  • phagocytosis
  • heat production
69
Q

anatomy of liver

A
  • largest internal organ
  • located in upper right quadrant of the abdomen
  • sits under the diaphragm & protected by rib cage
  • right kidney posteriorly located, stomach to right, colon inferior
70
Q

lobes of the liver

A
  • right lobe (large)
  • left lobe (smaller)
  • caudate lobe
  • quadrate lobe

(inferiorly: right lobe also includes the caudate and quadrate lobes)

71
Q

role & location of the falciform ligament

A
  • between right and left anterior lobe
  • attaches the liver to the anterior abdominal wall
72
Q

porta hepatis

A
  • main site where structures enter and leave the liver
  • structures include: portal triad, nerves & lymphatics
73
Q

3 structures of the portal traid

A
  • hepatic artery
  • hepatic portal vein (entering liver)
  • bile duct (leaving liver)
74
Q

liver blood supply

A

dual blood supply:
- hepatic artery -> from coelic trunk of aorta (supplies most organs), main blood supply, carries nutrients / toxins absorbed by GI tract
- hepatic portal vein -> convergence of veins draining the GI tract, smaller, provides oxygen rich blood, brings blood to liver before the heart to allow blood to be processed

75
Q

venous drainage of the liver

A

after blood passes through liver -> drained into the inferior vena cava by 3 hepatic veins

76
Q

hepatic portal system

A
  • blood draining from GI tract, pancreas and spleen carried to the liver first
  • key for delivery of nutrients / toxins for processing & hormone signalling
77
Q

what does a portal system do?

A

(blood related) connects one organ to another without returning to the heart first

78
Q

hepatocytes

A
  • make up 75-80% of liver cells
  • play role in metabolism, detoxification and amino acid synthesis
  • seperated from sinusoids by space of disse
  • membranes of hepatocytes facing the space of disse have microvilli for large s.a for better absorption
79
Q

sinusoids

A
  • specialised capillaries (leaky)
  • large, low pressure vessels
  • drain blood from hepatic artery & hepatic portal vein into the central vein
  • consist of fenestrated epithelium: facilitate the transfer of metabolites between plasma and hepatocytes
  • contain kupffer cells
80
Q

stellate cells

A
  • in space of disse
  • inactive in healthy conditions
  • cause fibrosis in disease states
  • store vit A
  • produce collagen when activated
81
Q

kupffer cells

A
  • in sinusoids
  • specialised macrophages
  • form part of the reticuloendothelial system (breaks down rbcs)
  • help recycle rbcs
82
Q

liver lobules

A
  • each lobe in liver made up of thousands of lobules
  • hepatocytes and vessels of liver arranged in hexagons with branches of the portal traid at each corner + a central vein
  • bile canaliculi run in a network between hepatocytes -> receive bile secretions + join to form small bile ducts
  • blood supply from hepatic artery and hepatic portal vein enter via sinusoids
83
Q

phases of drug metabolism / detoxification

A
  • 1: modification
  • 2: conjugation
  • 3: excretion
84
Q

phase 1 - modification

A
  • mainly done by cytochrome P450 enzymes (in smooth ER of hepatocytes)
  • enzymatic incorporation of polar groups (O or OH)
    • oxidation
    • reduction
    • hydrolysis
  • act as a handle for conjution phase
  • can produce metabolites that are very reactive and toxic (e.g. paracetamol)
85
Q

phase 2 - conjugation

A
  • addition of an ionised group (e.g. glutathione, sulfate, glycine, glcoronic acid)
  • occurs in cytoplasm of hepatocytes
  • makes metabolite water soluble for transport
  • inactivates the metabolite (drug inactive = safe)
86
Q

phase 3 - excretion

A
  • smaller metabolites excreted by kindey
  • larger ones in bile
87
Q

bilirubin

A
  • a yellowish substance made during your body’s normal process of breaking down old red blood cells
  • broken down by macrophages to bilirubin
  • free bilirubin can be toxic if crosses into blood brain barrier
  • bound to albumin in plasma to be transported to the liver
  • excess bilirubin = jaundice (yellowish skin + eyes)
88
Q

bilirubin excretion

A
  • when bilirubin is conjugated to glucuronic acid it forms bilirubin glucuronide
  • conjugated bilirubin: more soluble + can be excreted by the hepatocyte into the biliry canaliculi
89
Q

carbohydrate metabolism

A
  • liver helps maintain a normal blood glc level
  • necessary for brain, ns + energy
  • hormones regulate the way the liver maintains proper blood glc:
    -> insulin (anabolic)
    -> glucagon (catabolic)
90
Q

what happens when there is high blood glc?

A
  • increased glc uptake via the GLUT2 receptors
  • insulin is released from the pancreas
  • more glc retained by hepatocytes
  • glc -> glucose-6-phosphate (G6P) via glucokinase
  • liver converts G6P -> glycogen via glycogen synthase (glycogenesis)
  • increased triglyceride synthesis
91
Q

what happens when there is low blood glc?

A
  • glucagon released from pancreas
  • liver converts glycogen -> glucose-1-phosphate via glycogen phosphorylase
  • G1P -> glc via phosphoglucomutase
  • gluconeogenesis: synthesis of glc from aa and triglycerides in an 11 enzyme catalysed reaction that needs ATP and GTP
92
Q

lipid metabolism

A

synthesis of triglycerides:

  • excess glc, acetyl CoA -> fatty acid synthesis
  • storage in liver or transported to adipose tissue and muscle as VLDL
  • phospholipids

synthesis of cholesterol:

  • base for steriod hormone production (cortisol, testosterone)
  • cell membranes
93
Q

protein metabolism

A
  • synthesis of all non-essential a.a
  • synthesis of almost all plasma proteins (albumin, clotting factors)
  • deamination -> removal of amino group from a.a -> energy production (ammonia produced)
  • urea cycle: processing of toxic ammonia to urea for excretioon
94
Q

liver regeneration

A
  • mature hepatocytes can undergo cell division / mitosis -> maintain number of healthy cells
  • severe injury -> activation of liver progenitor stem cells -> can differentaite into other cell types (e.g. that line the bile ducts)
  • can lead to chronic diseases
  • healthy liver is smooth
  • sorosis = scarring
95
Q

function of the kindeys

A
  • HOMEOSTASIS
  • disposal of waste from the body
  • osmoregulation / balance of ions
  • regulation of blood volume & pressure (bore blood vol = higher bp)
  • regulation of blood pH
  • hormone production
96
Q

anatomy of renal system

A
  • ureters
  • bladder
  • urethra
97
Q

anatomy of kidneys

A
  • posterior wall of abdomen (towards the back)
  • retroperitoneal (behind peritoneal membr)
  • either side of vertebral column
  • around level of 12th rib
  • left slightly higher
98
Q

kidney blood supply

A
  • directly from aorta (heart) via renal arteries
  • returned to inferior vena cava via renal veins (back to heart)
  • get 20-25% of restin caridac output
  • blood supply needed as their role is to filter blood
99
Q

nephrons

A
  • makes up cortex and medulla
  • functional units of the kidneys
  • comprise a renal corpuscule and renal tubule
  • needed for ultrafiltration of blood and reabsorption / excretion
  • 1.3 million in each kidney
100
Q

renal corpuscle

A
  • each nephron consists of a renal corpuscle and a renal tubule
  • where blood plasma is filtered
  • lies within renal cortex
  • consists of glomerulus and bowman´s capsule
  • inner visceral layer: wraps around the endothelial cells of glomerular capsule
  • outer parietal layer: forms outer wall of capsule
101
Q

what is unusaul about the blood supply to the renal corpuscle?

A
  • it is drained and supplied by arterioles
  • efferent + afferent arterioles
  • arterioles can control the blood flow & pressure in & out of the capillary beds
  • lower bp = less blood filtered into bowman´s capsule
102
Q

glomerulus

A
  • specialized bundle of capillaries that are uniquely situated between two resistance vessels
  • filtration
103
Q

bowman´s capsule

A
  • double walled cup of epithelial cells
  • a part of the nephron that forms a cup-like sack surrounding the glomerulus
104
Q

capuscular space

A

area between 2 layers of nephron

105
Q

ultrafiltration

A
  • glomerular fitration = first step of urine production
  • water + most solutes in blood plasma pass from glomerular capillaries to glomerular capsule (glomerular filtrate)
  • filters 180l/day
  • elimate 2l of urine a day
  • glomerular capsule drains into renal tubule
106
Q

renal tubule

A

consists of:
- proximal convoluted tubule
- loop of henle (extends into renal medulla)
- distal convoluted tubule (within renal cortex)
needed for reabsorption / secretion

107
Q

proximal convoluted tubule

A
  • largely responsible for reabsorption of glc, sodim & other solutes
  • where most of the nutrients are absorbed back into the body
108
Q

loop of henle

A
  • counter current multiplier
  • creates osmotic gradiant + dilute urine
109
Q

distal convoluted tubule

A

reabsorbes water from filtrate

110
Q

counter current multiplier

A
  • The loop of Henle utilizes the countercurrent multiplier system to increase the concentration of solute and ions within the interstitium of the medulla.
  • This ultimately allows the nephron to reabsorb more water and concentrate the urine while at the same time using as little energy as possible.
  • higher solute conc deeper in medula -> water moves out of filtrate via the osmotic gradient
111
Q

regulation of the kindeys - ADH

A

anti-diuretic hormone (ADH)

  • stimulates insertion fo aquaporin channels
  • increases water permeability
  • more water reabsorbed = urine more concentrated
  • low ADH = water diuresis
  • ADH is a vasocontrictor / vasopressin
  • ADH increases blood pressure
112
Q

regulation of kidneys - renin-angiotensin-aldosterone system

A

angiotensinogen -> angiotensin I (renin in kidney) -> angiotensin II (ACE) -> aldosterone + Na+/H2O retention + ADH in post pit + systematic vasoconstriction

  • RAAS: controls blood pressure
  • lead to increase in blood volume + pressure
  • if RAAS overactive -> hypertension
113
Q

regulation of kindeys - sympatheic NS

A
  • can decrease Na+ and water excretion
  • can increase angiotensin 2 formation
114
Q

regulation of kindeys - parathyroid hormone

A
  • increase reabsorption of calcium in DCT
115
Q

regulation of kidneys - natriuretic peptides

A
  • atrial natriuretic peptide (ANP)
  • brian natriuretic peptide (BNP)
  • c-type natriuretic peptide (CNP)
116
Q

what regulates the kindeys?

A
  • anti-diuretic hormone
  • renin-angiotensin-aldosterone system
  • sympathetic NS
  • parathyroid hormone
  • natriuretic peptides
117
Q

how does the mucosa lining the oral cavity protect against friction?

A
  • mucosa lining in oral cavity made from stratified squamous epithelium
  • epithelium is thick -> protects underlaying layers from damage
  • extra protection by keratinized stratified squamous epithelium og hard palate and gums
  • keratin is tough & makes the epithelium stronger, reducing impact of friction
118
Q

what is the rugae of the stomach?

A

-internal folds
- stretch to accomodate more food

119
Q

muscles in the stomach

A
  • three different oreintations
  • allow food to be mixed more thoughroighly with the stomach acid
  • allows for greater breakdown of food into molecules to then be absorbed as pass through small intestine
120
Q

the muscularis externa

A
  • made of two layers
    inner layer = circular mucle fibres
    outer layer = longitudinal fibres
  • in oesophagus and small intestine
121
Q

what is bile?

A
  • digestive secretion
  • constains bile salts, bilirubin, cholesterol, neutral fats, phospholipids & electrolytes
  • bile helps assimilate lipids
  • gets rid of unwanted substances
  • neutralises gastric acid
  • provides optimum pH for pancreatic enzymes
122
Q

which hormones are released during the intestinal phase of digestion?

A
  • cholecystokinin (CCK) & secretin
  • inhibit gastric secretions
123
Q

where does the common bile duct pass fluid from?

A
  • cystic duct (gallbladder)
  • hapatic duct (liver)
124
Q

how does bile enter the small intestine?

A

via the major duodenal papilla

125
Q

function of pancreatic acini

A

secrete digestive enzymes

126
Q

How do the plicae circulares, villi, and microvilli contribute to the function of the small intestine?

A
  • increase surface area of mucosa avaible for digestion and absorption
  • nutrients are then absorbed into the blood stream (via capillaries in villi) and lipids absorbed into lymph (via lacteals in villi)
127
Q

why is the small intestine the longest organ of digestice tract?

A

longer = more s.a. = more absorption

128
Q

what are the 3 main areas of lipid breakdown in GI tract? which 3 enzymes involved?

A
  • mouth: lingual lipase
  • stomach: gastric lipase
  • small intestine: pancreatic lipase (main one in adults)
129
Q

how is a hepatic lobe structured?

A
  • stacked hepatocytes that radiate out from a central vein
  • hepatocytes form “walls”
130
Q

what processes are hepatocytes involved in?

A
  • protein synthesis and storage
  • detoxification
  • synthesis of cholesterol, bile salts and phsopholipids
  • transform and store carbs
131
Q

function of the renal pelvis

A

receives urine from major calyces & carries it towards the ureter

132
Q

effect of increas anti-diuretic hormone on urine production.

A
  • stimulates insertion of aquaporin channels
  • increases water permeability
  • urine more concentrated

human biology (11 decks)

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