Digestive Tract

Describe how gastric functions is regulated with its three phases

1- swallow - stomach relaxes 2- food stretches stomach 3- peristalsis is kept in rhythm by pacemaker cells Phase 1 - cephalic sight smell thought taste gastric secretions and motility Phase 2 - gastric phase prescence of food/protein secretion stimulated phase 3 - intestinal phase dudenum regulates activity with hormones and reflexes

Describe the gross anatomy of the large intestine

1.5m long and 6.5cm in diameter Begins with cecum, ascending, transverse and descending colon, sigmoid colon, rectum

describe how eat major class of nutrient is chemically digested and name the enzymes involved

Carbohydrates - digested by amylase starting in mouth and ceases in stomach. Pancreatic amylae digest it further in small intestine. Proteins - digested by pepsin in the stomach and ceases in the small intestine, but pancreas release trypsin and chymotrypsin. Fats - Lecithin emulsifies fate with bile. then acted upon by lipase

Describe the gross and microscopic anatomy of the small intestine

Duodenum - 25cm - liver empties neutralises acids Jejunum - 2.5 metres - most digestion occurs here Ilieum - 3.6metres - clusters of lymphatic nodules Surface area- •circular folds/pilae circularis 10mm tall •vili project 1mm outwards for absorption •microvilli cover surface Crypts- •pore exist between villi secrete intestinal juices (1-2L daily)

Describe how each nutrient is absorbed by the small intestine

Glucose - transported then diffused fructose - diffused entirely galactose - transported then diffused proteins - diffused entirely fats - diffused entirely

Identify and describe the four wall layers of the digestive tract

Innermost: mucosa -epithelium -lamina propria -muscularis mucosae Sub mucosa Muscularis externa -inner circular layer -outer longitudinal layer Adventitia or Serosa -arelar tissue or mesothelium

describe the gross and microscopic anatomy of the stomach

J shape organ, inner curvature is called the lesser curvature and the outer is called the greater curvature. the stomach has four regions:funds (top) cardiac (oriface) body (main portion) pyloric (narrow inferior) Its microscopic layers include: inner mucosa submucosa muscularis externa serosa

Give three examples as to why the stomach does not digest itself

Mucous coat Rapid epithelial cell replacement Tight junctions prevent self digestion

Describe the neural control of salivation and swallowing

Parasympathetic stimulation - salivary glands produce it, in enzymes (Ach) Sympathetic stimulation - produce less abundant saliva, more mucous

Define peritoneum and peritoneal cavity and describe the relationship of the digestive organs to the peritoneum

Peritoneum: serous membrane of the abdominal cavity: visceral and parietal Peritoneal cavity: lubricates digestive organs allows them to slide across one another Peritoneal organs (intraperitoneal) - organs surrounded by peritoneum Retroperitoneal organs organs outside the peritoneum

Describe the composition and functions of saliva

Saliva functions include: •moistening of food •initiate starch fat digestion •cleanse teeth •inhibit bacteria •bind find into bolus Saliva is a hypotonic solution (99.5% water) Saliva is released by parasympathetic and sympathetic reflexes

Describe the general neural and chemical controls over digestive function

The digestive system function is controlled by the autonomic nervous system. there are sympathetic and parasympathetic pathways. the enteric nervous system is two networks of neurons that controls local motility and secretion in the gastrointestinal tract. It is independent of the ANS, but is regulated by the ANS activity. The two enteric nerve networks are: •the submucosal plexus - secretion •the myenteric plexus - peristalsis

State how the mocosa of the small intestine differs form that of the stomach and explain the functional significance of the differences

The mucosae of the small intestine involves the submucosa and form the plicae circulars that effectively increase the surface area of the intestines.

Describe the gross anatomy of the digestive tract from the mouth to the anus

Without tone, the digestive tract stretches up to the 9 metres. Mouth Pharynx - Oropharynx then Laryngopharynx Oesophagus stomach - Fundic then body then pyloric small intestine: -duodenum -jejunum -ileum large intestine -appendix -cecum -ascending colon -transverse colon -descending colon rectum anus

Explain how hormones regulate secretions of the liver and pancreas.

cholecyctokinin - released from duodenum in respond to arrival of acid and fat. contracts gall bladder, secretions of pancreas, relaxation of hepatopancreatic sphincter secretion - released from duodenum in response to acidic chyme. secretions of bicarbonate neutralises chyme gastrin - from stomach and duodenum stimulates galls bladder contraction and pancreatic enzyme secretion

Describe the six essential activities of the digestive tract

ingestion mechanical digestion propulsion chemical digestion absorption defeacation

describe the types of movement that occur in the small intestine

intestinal motility includes: •mixing of chyme - segmentation •churning of chyme - segmentation •movement of residue - peristalsis

Describe the gross anatomy (microscopic too) of the liver, gall bladder, bile duct system and pancreas

liver: four lobes, right, left, caudate, and quadrate falciform ligament joins right and left lobes. round ligament is remnant of umbilical cord made up of hepatic tubules each has a central vein surrounded by hepatocyte cells, separated by sinusoids and fenestrated epithelium gall bladder: adheres to inferior suface between right and quadrate lobes. cultic duct joins hepatic duct forming bile duct. gall bladder sotres and concentrates bile. Pancreas: retroperitoneal gland posterior to stomach. secretes insulin and glucagon into blood stream acini secrete enzymes and zymogens. zymogens - trypsinogen, chymotrypsinogen, protease enzymes.

contrast the large intestines mucosa with the small intestines

mucosa - simple columnar epithelium with no villi, plicae circularis to increase surface area. but does contain crypts

Name the four cell types found in the gastric mucosa and state their functions

mucous cells: secrete mucous for protection Parietal cells: secretes H+ and Cl- ions Chief cells: secrete pepsinogen Enteroendocrine cells: secrete gastrin

Explain the neurological control of defecation

strech recpetors signal intrinsic defecation, via the myenteric plexus. propriatic sensory receptors signal parasympathetic defecation via spinal cord voluntary control over outer sphincter occurs

discuss types of contractions that occur in the colon

takes 12-24 hours haustral contractions, 30 minutes mass movements 1-3 times a day

Name the accessory organs of the digestive tract

teeth tongue gall bladder salivary glands liver pancreas

State the physiological significance of intestinal bacteria

the bacteria ferment cellulose and undigested carbohydrates and synthesise vitamins b and k