Chapter 26- Digestive System Lecture

what are the accessory organs of the digestive system?

salivary glands, liver, gallbladder, pancreas, teeth, and tongue

how many layers are apart of the GI tract

4 layers

what is the first layer of the GI tract and what does it do?

mucosa- epithelium, lamina propria, and muscular mucosa. is the first line of defense

what is the second layer of the GI tract and what does it do?

submucosa- blood/lymph vessels, nerves, mucus secreting glands, MALT, and peyers patch in the S.I

what is the third layer of the GI tract and what does it do?

muscularis- consists of an inner (circular fibers to form sphincters), and an outer (longitudinal fibers) to create contractions throughout GI tract

what is peristalsis?

wave-like contractions that propel materials through the GI tract (milking contents towards the colon)

what is mixing?

blends the ingested materials and secretions of the GI tract together with ring-like contractions

what is the fourth layer of the GI tract and what does it do?

serosa- made of CT as the outermost layer

where are digestive structures below the diaphragm contained

in the peritoneum, which is lined by the serous membrane

* visceral attaches to organs, and parietal is the outermost lining

how does the parasympathetic nervous system regulate the GI tract?

it promotes GI tract activity by increasing motility and relaxing sphincters

how does the sympathetic nervous system regulate the digestive system?

it inhibits GI tract activity by decreasing motility and contracting sphincters

what do mechanoreceptors detect in the digestive system versus chemoreceptors?

**mechanoreceptors** detect if there is any food at all stretching the organs of the digestive system, where as **chemoreceptors** detect what kind of chemicals are in the food being digested.

what are the 3 primary hormones of digestion and were do they comes from?

1. gastrin- from the stomach
2. CCK (cholecystokinin)- from the SI
3. secretin- from the SI

what is the first step of the digestive process?

food is ingested and masticated

what are the 3 pairs of salivary glands in the mouth?

1. parotid- located behind ear and duct empties by the ear
2. sublingual- duct empties under the tongue also where it is located
3. submandibular- duct empties under the jaw, also where gland is located

what does saliva consist of?

salivary amylase, IGA, mucus, lysozyme. acts as first line of defense

what are the three phases of swallowing (Deglutition)

1. voluntary phase- in oral cavity passing oropharynx
2. involuntary phase 1-passes the entirety of the pharynx
3. involuntary phase 2- passes by the esophagus allowing larynx come up and close epiglottis

where does the esophagus pass through the diaphragm?

at the esophageal hiatus, the inferior esophageal sphincter allows the bolus to move in to the stomach and prevent regurgitation

how does the stomach get supplied with blood?

L gastric artery from the abdominal aorta and the R gastric artery from the hepatic artery create an anastomoses

what are the four primary regions of the stomach?

1. cardia- inferior esophageal sphincter entryway
2. fundus- like a superior dome
3. body- central area
4. pylorus- pyloric sphincter exit way

\*THINK: Can Freddy Buy Pickles?

how many secretory cells types are there in the stomach?

5

what are surface mucous cells and what do they secrete?

they secrete alkaline mucin that protects stomach lining from acid

what are mucous neck cells and what do they secrete?

they secrete acidic mucin helps contributes some acidity in the stomach

what are parietal cells and what do they secrete?

they secrete intrinsic factor which helps to absorb vitamin B12, as well as H+ and Cl- to form HCl within the stomach to form the acidic enviornment of the stomach

what are chief cells and what do they secrete?

they secrete pepsinogen which is the inactive form of enzyme pepsin which breaks down big proteins, as well as gastric lipase which can only function in more neutral environments so it has a limited role

what are G-cells and what do they secrete?

they secrete gastrin which is a hormone sent to the brain to stimulate chief and parietal cell activity and muscular contraction of the stomach

what are the three phases of gastric regulation?

1. cephalic phase- in this phase sensory input of food allows the medulla oblongata/hypothalamus to stimulate the stomach to increase force and speed of contractions
2. gastric phase- initiated by food in the stomach, baroreceptors detect stomach stretch and chemoreceptors detect chemical intake allowing stomach contractions to continue
3. intestinal phase- initiated by the Prescence of acidic chyme in the duodenum, this lower pH will send less hunger signals to the brain which will slow down contractions and stomach secretions

what are the 3 sections of the small intestine?

1. duodenum- shortest, but receives acidic chyme from the stomach, bicarb and juices w/enzymes from pancreas, and bile from gallbladder
2. jejunum- chemical digestion making big macromolecules smaller
3. ilium- absorption of digested nutrients. ileocecal valve at the end sending contents to large intestine.

how is the histology of the small intestine unique from the histology of the rest of the GI tract?

the SI contains villi formed by microvilli making a brush border. the simple columnar epithelium in each villi as well as blood/lymph capillaries inside allow substances to be absorbed. enzymes can be secreted from here too

what is secreted from this brush border in the SI?

CCK, secretin, mucus, H2O, enzymes from the microvilli breaking down small polymers into monomers.

where is bile produced and what does it do?

the liver produces bile, then drained to the gallbladder for storage and released into the duodenum.

bile allows for emulsification to occur which is the only way lipids can be digested

when does glycogenesis occur?

when blood glucose is high, excess glucose can be placed into glycogen reserves

when does lipogenesis occur?

when the reserves of glycogen are too full, so the glucose must be stored as fat.

when does glycogenolysis occur?

when blood sugar is low, glucose breaks out of glycogen reserves and is sent to blood

when does gluconeogenesis occur?

when your body has to make new glucose out of protein

what else does the liver do?

vitamin/mineral storage, detoxification of alcohol, phagocytosis of RBCs and synthesis of plasma proteins

what does the gallbladder do?

stores and concentrates bile, by being secreted via the cystic duct into duodenum

what does the pancreas do?

secretes pancreatic juice for digestion in the duodenum, being released via the pancreatic ducts

what does pancreatic juice contain?

bicarb to neutralize incoming chyme, and enzymes for digestion

what do proteases do?

finishes the job of stomach pepsin by breaking down large polypeptide chains into small polypeptide chains before brush border enzymes make small polypeptides into a monomer

what do carbohydrase’s do?

pancreatic amylase breaks down starches and carbs from larger polypeptide chains into smaller polypeptide chains

what do lipases do?

help to breakdown fats after they have been emulsified by bile into fatty acids and glycerol

what are CCK and Secretin?

CCK- secreted from SI and regulates the pancreas to by increasing pancreatic juice release and gallbladder contraction

Secretin- is secreted by the SI and regulates the pancreas to increase bicarb release

what are the regions of the large intestine in order?

1. cecum
2. ascending colon
3. transverse colon
4. descending colon
5. sigmoid colon
6. rectum
7. anus

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what are haustra?

pockets in the large intestine that help to move materials through

what do the intestinal bacteria in the large intestine do?

they help digest remaining nutrients, produce vitamin K, breakdown remnants that contribute to feces odor and color

what is feces made of?

H2O, salt, sloughed off epithelial cells, undigested foods and bacteria

what does high dietary fiber encourage?

high fiber in your diet allows for an increased size bulk, so the colon to stretch further stimulating colon movements

what are the two sphincters involved in defecation that create the defecation reflex (urge)

1. internal anal sphincter- under involuntary control
2. external anal sphincter- under voluntary control

how are amino acids absorbed?

amino acid moves into the cell through a symporter driven by sodium potassium pump. then they move out of the cell and enter the capillaries of the intestinal villi and go to the liver via hepatic portal vein

how are monosaccharides absorbed?

monosaccharides moves into the cell through a symporter driven by sodium potassium pump. then they move out of the cell and enter the capillaries of the intestinal villi and go to the liver via hepatic portal vein

how are lipids absorbed?

emulsified fats from bile become micelles and enter the intestinal cell through simple diffusion. once they are in the cell, they become separated into glycerol and fatty acid and combined into a triglyceride. Proteins will come and coat the triglyceride to make it water soluble, and go through the lymphatic system to the left subclavian vein where they are later stored by the liver as adipose tissue