Homeostasis lecture 7

winniesmith1's version from 2017-05-30 18:44

Section 1

Question Answer
What mechanisms prevent destruction of GIMucous lining, secretion of protease as pro enzymes activated in gut, weak acid in parietal cells, local endocrine and central control mechanisms (buffers)
Regions of the small intestineDuodenum,jejunum, lleum.
5 hours transit through small intestine . 90% of nutrient absorption occurs.
Describe the duodenumFirst bit,25cm long, neutralises chyme from stomach. receives secretion from pancreas and liver, neutralises stomach acid
few pelican circulares (permanent longitudinal folds)
small villi (fingerlike projections in mucosa, covered by columnar epithelium with microvilli).
Describe the Jejunum2.5 m long
Location of most chemical digestion and nutrient absorption
Prominent plica circulares and villi
Describe the lleum3.5 m long
Lympoid nodules (Peyer’s patches).
Ends at ileocaecal valve
Organisation of intestinal wall
lecture 7 pg 4
4 layers (top to bottom) Mucosa (villi) Muscularis mucosae, submucosa (has submucosal artery and vein, lymphatic vessel, submucosal plexus), muscularis externa (circular layer of smooth muscle, followed by myenteric plexus, then longitudinal layer of smooth muscle), serosa.
Internal structures of single villus

Has capillary and lymphatic supplies. External columnar epithelial cells with intermittent mucous cells.
Lamina propria - a thin layer of loose (or dense irregular) connective tissue, which lies beneath the epithelium and together with the epithelium constitutes the mucosa- rich in lymphocytes.
Each villus surrounded by brush border

Section 2

Question Answer
Intestinal glands (and 2 types)Epithelial cells divide at base are displaced towards tips of villi then disintegrate adding enzymes to lumen.
2 types: Brush border enzymes and enteroendocrine cells.
Brush border enzymesIntegral membrane proteins on intestinal microvilli
Break down materials in contact with brush border
Activates pancreatic proenzyme trypsinogen
Enteroendocrine cellsProduce hormones e.g. gastrin, cholecystokinin (CCK), and secretin
Duodenal glandsProduce mucus- raises pH
Intestinal juiceMoistens chyme and keeps intestinal contents in solution
Buffers acids

Section 3

Question Answer
Intestinal movements-Local reflexes- weak myenteric reflexeslocal. Enhanced by parasympathetic stimulation.
Intestinal movements -central controlParasympathetic stimulation increases motility and secretion.
Sympathetic stimulation inhibits.
Intestinal movements- central gastric reflexesMade up of the gastroenteric reflex and the gastroileal reflex.
Gastroentric reflexstimulates motility and secretion along the entire small intestine.
Gastroileal reflextriggers the opening of the ileocaecal valve, allowing materials to pass from the small intestine into the large intestine.
Ileocaecal valvecontrols the passage of materials into the large intestine

Section 4

Question Answer
The pancreas structure
lecture 7 pg 8
Lies posterior to stomach, from duodenum toward spleen (tucked into a C-shaped curve of the duodenum that begins at the pylorus of the stomach) Is bound to posterior wall of abdominal cavity. Is wrapped in thin, connective tissue capsule.
Pancreas functionsEndocrine cells (1%) of the pancreatic islets, secrete insulin and glucagon into bloodstream.
Exocrine cells: Acinar cells and epithelial cells of duct system secrete pancreatic juice.
Pancreatic juice1000 mL per day secreted by exocrine cells
Controlled by hormones from duodenum e.g. secretin, CCK
Contain pancreatic enzymes, including:
+Pancreatic alpha-amylase
+Pancreatic lipase
+Proteolytic enzymes
Proteolytic enzymes70% of all pancreatic enzyme production, including:
-Secreted as inactive proenzymes, activated after reaching small intestine

Section 5

Question Answer
The liverProduces bile to break down fat, the largest visceral organ in body (1.5kg; 3.3lb), regenerative.
Lies in right hypochondriac and epigastric regions, extends to left hypochondria and umbilical regions.
Anatomy: wrapped in tough fibrous capsule, covered by visceral peritoneum, divided into lobes.
Liver hepatic blood supply2/3 blood from hepatic portal vein, originating from: oesophagus, stomach, small intestine, much of large intestine.
1/3 blood from hepatic artery proper.
2nd capillary, hepatic vein
Histology of the liver100,000 hexagonal lobules (functional unit of liver)
1mm diameter, each lobe divided by connective tissue.

Each lobule has 6 Portal areas which contain:
-Branch of hepatic portal vein
-Branch of hepatic artery proper
-Branch of bile duct
Blood flow in hepatocytes.Blood flows past hepatocytes, absorbs solutes and secretes proteins.
Drains into:
-Sinusoids>central vein
-Bile ductules> bile ducts.
Functions of the liver: metabolic regulation-Carbohydrate metabolism (stabilise glucose, glycogen store, gluconeogenesis)
-Lipid metabolism (regulation of circulating triglycerides, fatty acids, cholesterol)
-Amino acid metabolism (storage: deamination)
-Waste product removal (neutralises ammonia and other toxins)
-Vitamin storage (fat soluble vitamins (A,D,E,K), B12
-Mineral storage (ferritin)
-Drug inactivation
Functions of the liver: haematological regulation-Largest blood reservoir in the body.
-Receives 25% of cardiac output.
-Phagocytosis and antigen presentation
-Synthesis of plasma proteins
-Removal of circulating hormones, antibodies, toxins
Liver functions: bile production-Bile salts break insoluble lipid droplets apart (emulsification)
-Increases surface area exposed to enzymatic attack

Section 6

Question Answer
Bile transport from liver to gallbladder/duodenum+Liver secretes bile fluid:
Into a network of narrow channels (bile canaliculi)
Between opposing membranes of adjacent liver cells
Right and Left Hepatic Ducts
Collect bile from all bile ducts of liver lobes
Unite to form common hepatic duct that leaves the liver
+Bile Flow
From common hepatic duct to either:
The common bile duct, which empties into duodenal ampulla (with pancreatic duct)
The cystic duct, which leads to gallbladder
Physiology of the gallbladder-Stores bile
-Releases bile into duodenum, but only under stimulation of intestinal hormone cholecystokinin (CCK)
-Without CCK:
Hepatopancreatic sphincter remains closed.
Bile exiting liver in common hepatic duct cannot flow through common bile duct into duodenum.
Bile enters cystic duct and is stored in gallbladder.

1) liver secretes bile continuously- roughly 1L per day.
2) As it remains in the gallbladder, bile becomes more concentrated.
3) Release of CCK by the duodenum triggers dilation of heptopancreatic sphincter and contraction of gallbladder. This ejects bile into the duodenum through duodenal ampula.
4. In the lumen of the digestive tract, bile salts break the lipid droplets apart for emulsification.
Hormonal control

Diagram pg 17
Secreted by stomach & duodenal G cells when exposed to incompletely digested proteins
Increases stomach motility, stimulates acids and enzyme production

Gastric Inhibitory Peptide (GIP):
Secreted when fats and carbohydrates enter small intestine; inhibits gastrin activity

Released when chyme arrives in duodenum
Increases secretion of bile and buffers by liver and pancreas

Cholecystokinin (CCK):
Secreted in duodenum in response to lipids and partially digested proteins
Accelerates pancreatic production and secretion of digestive enzymes & relaxes hepatopancreatic sphincter and gallbladder
Inhibits gastric activity, in CNS promotes satiety

Vasoactive Intestinal Peptide (VIP):
Stimulates secretion of intestinal glands, Dilates regional capillaries, Inhibits acid production in stomach

Is released when chyme enters small intestine
Stimulates mucin production by submucosal glands of duodenum
The large intestine1.5 meters (4.9 ft) long and 7.5 cm (3 in.) wide
Function of the large intestine-Absorption (<10% of all absorption):
Reabsorption of water
Reabsorption of bile salts in caecum
Absorption of vitamins produced by bacteria
Absorption of organic wastes
-Compaction of intestinal contents into faeces
-Storage of faecal material prior to defaecation
Regions/ gross anatomy of large intestine

Appendix leads into ceum-
Ileum leads into cecum- ileocaecal valve- ascending colon- transverse colon- descending colon- sigmoid colon- rectum.

In square shape around blood vessels.
Histology of large intestine
-Lacks villi
-Abundant mucous cells
Dominated by mucous cells.
-No enzymes
-Large lymphoid nodules -scattered throughout lamina propria and submucosa
-The longitudinal layer of the muscularis externa =>taeniae coli

Section 7

Question Answer
Mucosa and glands of the colon: layersSimple columnar epithelium.

Goblet cells

Intestinal crypt

Muscularis mucosae


3 vitamins produced in large intestine1. Vit.K (fat soluble)
2. Biotin (water soluble)
3. Vit.B5 (Pantothenic acid)(water soluble)
Vitamin Kfat soluble.
Required by liver for synthesizing clotting factors.
Biotinwater soluble
Important for glucose metabolism
Vitamin B5Pantothenic acid. Water soluble.
Required in manufacture of steroid hormones and some neurotransmitters
Movements of the large intestine+Movement from caecum to transverse colon is very slow
-allows hours for water absorption
+Peristaltic waves move material; Segmentation mixes
+Movement from transverse colon through rest of large intestine results from powerful peristaltic contractions (mass movements)
-Stimulus is distension of stomach and duodenum; relayed over intestinal nerve plexuses
Defaecation relex+Distension of the rectal wall triggers defaecation reflex
-Positive feedback loops
-Triggered by stretch receptors in rectum

Section 8

Question Answer
Summary+The Processing and Absorption of Nutrients
+Breaks down physical structure of food
+Disassembles component molecules
+Molecules released into bloodstream are:
-Absorbed by cells
-Broken down to provide energy for ATP synthesis
-Or used to synthesize carbohydrates, proteins, and lipids
Water absorptionpg29