12. GASTROINTESTINAL TRACT (GIT) Accessory organs

Pancreatic juices contain

*Prolases: (LAP) lipase amalase protase *Sodium Bi-carbonate approximately 1200-1500ml of clear pancreatic juice is produced daily!!

Composition and Function of Pancreatic Juice

*Water solution of electrolytes, primarily HCO3- -neutralizes acid chyme -provides optimal environment for pancreatic enzymes *Enzymes are released in inactive form and activated in the duodenum

Composition of Bile

-A yellow-green, alkaline solution containing bile salts, bile pigments, Cholesterol, triglyceride's, phospholipids, and electrolytes -Bile salts are cholesterol derivatives that: * emulsify fat * facilitate fat and cholesterol absorption * help make cholesterol soluble -Enterohepatic circulation recycles bile salts -The main bile pigment is bilirubin (waste product of heme from RBC)

The Gallbladder

-Thin-walled, green muscular sac, about 10cm long, on the ventral (anterior) 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 and then the duodenum

Liver

A large solid organ that lies in the right upper quadrant of epigastric region, immediately below the diaphragm: The livers main function is to filter and process the nutrient rich blood delivered to it. It produces bile, stores glucose for immediate use by the body, and produces many substances that help regulate immune responses. Largest gland in the body, shaped like a wedge, 4 primary lobes, enclosed by the visceral peritonem.

Regulation of Bile

Acidic, fatty chyme causes the duodenum to release: -Cholecystokinin (CCK) and secretin into the bloodstream -Bile salts and secretin transported in blood stimulate the liver to produce bile -Vagal stimulation causes weak contractions of the gallbladder

Definition of hepatocyte?

Hepato = (Liver) : cyte = (cell) = liver cell

Liver: Microscopic Anatomy Hepatocyte functions?

Hepatocytes store glucose and glcogen, use amino acids to make plasma proteins, and detoxify metabolic wastes and drugs. Hepatocyte functions include: • continuous production of bile • processing blood borne nutrients • storage of fat-soluble vitamins • detoxification • Secreted bile flows between hepatocytes toward the bile ducts in the portal triads

Liver: Microscopic Anatomy liver lobules ?

Hexagonal-shaped liver lobules are the structural and functional units of the liver. Sesame seed sized. -Composed of hepatocyte (liver cell) plates radiating outward from a central vein -Portal triads are found at each of the six corners of each liver lobule

Parasympathetic Nerves

Involuntary, autonomic nerves that regulate normal body functions such as heart rate, breathing, and muscles of the gastrointestinal tract. Stimulation salivation (vagus + glossopharyngeal)- food, irritants, nausea

Sympathetic nerves

Prepare the body for emergencies and stress; fight or flight syndrome. Inhibits salivation

Gland Cells (of stomach fundus and body)

Produce majority of the stomach secretions Glands in these regions contain a variety of secretory cells: Mucous Neck Cells Parietal Cells Chief Cells Enteroendocrine cells

Mucous Neck Cells

Scattered in the "neck" and more basal region of the glands- produce a thin soluble mucus. Function of this acidic mucous is not yet understood.

Define: Secretion - Excretion - Enzyme - Alkaline -

Secretion - substances released or eliminated by cells or glands Excretion - eliminating, getting rid of substances Enzyme - catalyst in chemical reactions Alkaline - pH above 7, more basic/alkaline substances than acidic substances

Gastric glands

Simple tubular - produces gastric juice. Located in the lining of the stomach; secretes HCl and various enzymes (eg Pepsin) when stimulated by gastrin.

Regulation of Pancreatic Secretion

Vagal stimulation causes release of pancreatic juice CCK and secretin are released into the blood stream when fatty or acidic chyme enters the duodenum Upon reaching the pancreas: -CCK induces the secretion of enzyme-rich pancreatic juice -secretin causes secretion of bicarbonate-rich pancreatic juice

The function of the hepatic portal circulation is to ________.

collect absorbed nutrients for metabolic processing or storage

Which duct carries bile out of bile ducts in the liver?

common hepatic duct

Parietal Cells

found mainly in the more apical region of the glands scattered among chief cells, simultaneously secrete hydrochloric acid (HCl), and intrinsic factor. Structure bears dense microvilli which provides a huge surface area for secreting H+ and Cl- into the lumen. HCl makes stomach contents extremely acidic which is necessary for activation and optimal activity of protein- digesting enzyme pepsin.

What is a major function of pancreatic juice?

neutralizing chyme entering the small intestine from the stomach it is alkaline

Chief Cells

occur mainly in the basal regions of the gastric glands. Cuboidal shaped and produce pepsinogen which is the inactive form of the pepsin. Also secretes lipases (fat digesting enzymes).

What is the opening to the mouth called?

oral orifice

The __________ is the serous membrane that lines the abdominal body wall.

parietal peritoneum

The pancreas secretes __________.

procarboxypeptidase

Pancreas: Endocrine functions

produces and releases two hormones; glucagon and insulin to control blood sugar levels * Release of insulin and glucagon from Islets of Langerhans glucagon- raises your blood sugar levels/insulin - lowers your blood sugar levels

Pancreas: Exocrine functions

produces pancreatic juices which contain enzymes for digesting fats, carbohydrates, and proteins. Secretes pancreatic juice from acini (clusters of secretory cells surrounding ducts): digestive enzymes - breaks down all categories of foodstuffs (CHO, fats, proteins)

Enteroendocrine cells

typically located deep in the gastric glands, release a variety of chemical messengers directly into the interstitial fluid of the lamina propria. Histamine & serotonin act locally as paracrines others such as somatostatin act both as paracrines locally and as diffused hormones in the blood Gastrin, a hormone, plays essential roles in regulating stomach secretion and motility

Learning Outcomes:

• Describe the structure and function of the major organs of the gastrointestinal tract (revision) • Describe the composition and function of the fluids secreted by the GIT • Describe the structure and function of the accessory organs • Define the major processes occurring during GIT activity (revision)

Histamine

• site of production: Stomach mucosa • Stimulus for production: food in stomach Activity: • in the stomach = activates parietal cells to release HCl

Cholecystokinin (CCK)

• site of production: duodenal mucosa • Stimulus for production: Fatty chyme Activity: • In the Stomach = inhibits stomachs secretory activity • In Pancreas = increases output of enzyme-rich pancreatic juice • In the Gallbladder = stimulates organ to contract and expel stored bile • In the Hepatopancreatic sphincter = relaxes sphincter to allow entry of bile and pancreatic juice into duodenum

Secretin

• site of production: duodenal mucosa • Stimulus for production: acidic chyme (also partially digested proteins and fats Activity: • In the stomach = inhibits gastric gland secretion and gastric motility during gastric phase of secretion • In the Pancreas = increase output of pancreatic juice rich in bicarbonate ions; potentiates CCK's action • Liver = increases bile output

Gastrin

• site of production: stomach mucosa (G cells) • Stimulus for production: Food in stomach and acetylcholine released by nerve fibers Activity: • in the stomach- parietal cells = increases HCl secretion •stimulates gastric emptying (minor effect) • in the Small intestine = stimulates contraction of intestinal muscle • in the Ileocecal valve = relaxes ileocecal valve • in the Large intestine = stimulates mass movement