Exam 4 bio 163

Digestive System

Processes food, extracts nutrients, and eliminates waste

"Disassembly line"

breaks down complex molecules to simple forms we can absorb and use.

ingestion

intake of food

digestion

breakdown of food

absorption

uptake of nutrients into bloodstream

egestion

elimination of undigested food

Gastrointestinal tract (GI tract)

tube extending from mouth to anus , about 9 meters long; also called alimentary canal.

Accessory organs

aid in digestion by shearing food or secreting various substances into the GI (includes teeth, tongue, salivary glands, pancreas, liver, gallbladder)

Membranes of digestive system. (what layers)

Epithelial layer, areolar layer, acellular layer of fibers (basement membrane)

Peritoneal cavity

the space between the parietal and visceral serosa membrane

Mesenteries of digestive tract

double layers of serosa tissue found in peritoneal cavity

Mesenteries

double layers of peritoneum
- connect visceral peritoneum with parietal peritoneum
- hold organs in place
-prevent friction due to serous fluid
- fat cushions organs
- allows nerves and blood vessels to reach intraperitoneal organs without having to pierce through the peritoneum

GI tract tube consists of 4 layers of tissues named

-mucosa (secretion and absorption)
-submucosa (secretion, nervous tissue (plexus))
-Muscularis (motility, contains nervous tissue plexus)
-Serosa (same as peritoneum)

Mucosa layer contains 3 different tissue types
epithelium

- stratified squamous cells in mouth anus and esophagus
- simple columnar everywhere else
- secretes enzymes and absorbs nutrients
- specialized cells goblet secrete mucus
- specialized cells (enteroendocrine) secrete hormones
- these specialized. cells are grouped together in glands

Mucosa layer contains 3 different tissue types
Lamina Propria

Thin layer of loose connective tissue contains capillaries

Mucosa layer contains 3 different tissue types
Muscularis mucosae

-Very think layer of smooth muscle
- increases movement for digestion

Submucosa layer

contains cells arranged in glands, secretes subtances necessary for digestion

description of submucosa layer

- dense irregular or loose connective tissue
- contains blood vessel, glands and lymphatic tissue
-contains submucosal (meissner's) plexus
- involuntary nerves cause contraction of muscle layers
- stimulates secretion of hormones

Muscularis layer

helps with motility via peristalsisM

Muscularis layer description

Two smooth muscle layers--> involuntary
- circular toward lumen, longitudinal around circular
- helps with peristalsis
can be specialized skeletal muscle--> voluntary
-in mouth, pharynx upper esophagus and anus
- control swallowing or defecation
also contains myenteric plexus

Which layer of the GI tract comes into direct contact with food?

Mucosa

Which layers of GI tract will contribute to secretion?

Submucosa and mucosa

Functions of digestion

Food intake
-mechanical digestion (mastication)
- chemical digestion
-special sense- taste

Hard palate

Palatine bone and maxilla bone

Soft palate

Muscles covered in mucous membrane
stratified epithelial tissue

Salivary glands

Produces saliva that help with several processes related to digestion
-exocrine glands (contain ducts) submandibular gland produces the most.

role of saliva

-helps with lubrication
- chemical digestion = salivary amylase starts carbohydrate digestion
-special sense= flavor molecules dissolve in saliva

deglutition

swallowing (requires epiglottis)

Peristalsis

Muscle contractions

What type of epithelial cells line the pharynx and esophagus

Stratified squamous

what type of muscle is found in the muscularis layer of the esophagus?

mix of skeletal in upper part to smooth in lower part

The stomach role

-food storage
- can hold up to 4 liters of ingested material
-mechanical digestion
- grinding and pulverizing action
-initial chemical digestion
- primarily mostly proteins get digested in spanish
-sphincter control movement of food into and out of the stomach.

Movement of chyme is regulated by

sphincters

Lower esophageal (cardiac) role

control entry of food
(smooth muscle)

pyloric sphincter

control exit of chyme
- Smooth muscle

Inside the stomach - mucosa forms

rugae

Fuction of rugae

allow the stomach to expand

Why would you want more muscles in the stomach?

Improve mechanical digestion

Where are Gastric pits and glands located

Mucosa layer ,

Describe gastric pits and glands

The base of a pit splits into two or three gastric glands
( produce secretions, and is transported upwards to lumen of stomach)

Gastric secretions mix with food and saliva to make

chyme

What does mucous neck cells

secrete mucus

Chief cells secrete

pepsinogen
-> converted to pepsin by HCL
-> functions in protein digestion

Parietal cells secrete

hydrochloric acid (HCL)
- helps denature (unfold) proteins
- activates pepsinogen (like scissors)
- kills pathogens

2 major enteroendocrine cells that help regulate other cells and gastric/intestinal function

Gastrin and histamine

Gastrin stimulates..

parietal cells to release HCL and chief cells to release pepsinogenHi

Histamine further stimulates..

release of acid
decrease pH that leads to protein digestion

The pH of the stomach is

low ~ 2 (acidic)

what cells directly contribute to this pH?

Parietal cells

What cells indirectly contribute to stomach pH?

Gastric EE cells (travel to blood stream and then acts on cells

The small intestine

Chyme enters small intestine in a slow and controlled manner
- regulated by hormone and nervous system

First part of digestion in small intestine

Duodenum
-pancreatic juices and bile enters here

role of rest of small intestine (ileum and jejunum)

high surface area for absorption of nutrients

villi and microvilli help improve the....

surface area for absorption of nutrients

mucosa layer of the intestine has ______ similar to gastric pits

crypts

Mucosa layer of intestine is composed of

simple columnarD

what do crypts contain

-absorptive cells
- mucous - producing cells
- intestinal enteroendocrine cells that secrete

intestinal enteroendocrine (hormones) cells in crypts secrete what

- Gastric inhibiting peptide (GIP)
- inhibits stomach function and promotes insulin release
-secretin --> stimulate pancreas and liver, inhibit parietal cells
-Cholecystokinin (CCK)
- stimulates pancreas, liver , gallbladder and inhibits stomach function (triggers release of bile)

Which of the following characteristics distinguishes accessory organs from organs of the GI tract?

Food does not travel through accessory organs

Accessory organ - pancreas describe

Located by duodenum
- shares a common duct (entry point into duodenum with the gallbladder.

99% of the cells in the pancreas secrete

digestive juices (acinar cells)

1 % of the cells of the pancreas are responsible for secreting

insulin/glucagon ( cells of islets of langerhans)

Acinar cells connect to small ducts that drain into the pancreatic duct. This duct connects the pancreas with the duodenum what type of cells are acinar cells?

exocrine (cell connects to duct= exocrine)

Composition and function of pancreatic juices

-release of juices is stimulated by parasympathetic system and CCK and secretin
- contains a mixture of components
- water
- sodium bicarbonate --> neutralizes stomach acid
- enzymes---> help with digestion

Digestive enzymes
Pancreatic amylase digests

starch

Pancreatic lipase digests

fat

proteases digest

proteins

Nuclease digest

nucleic acids

Acessory organ liver function

-Largest gland in the body
function to
- metabolism of digested nutrients
- detoxifies alcohol/ drugs
-produces bile
A

Accessory organ : gallbladder

Bile is secreted by liver cells transported and stored in the gall bladder
gall bladder will release bile into the duodenum

Gallbladder function

Neurons and hormones will stimulate the muscularis layer to contract and release bile into the duodenum

Release of bile and composition

Gall bladder is stimulated by parasympathetic system and CCK and secretin to release bileC

Composition of bile

-Bile salts ---> digestion
helps with fat break down
-cholesterol -->waste
-produced in and removed by liver as waste
-Bile pigments (bilirubin) from hemoglobin--> waste
globin= a reusable proteein
heme= broken down into iron and bilirubin
-bilirubin is toxic and must be removed

Pancreatic juices are secretion into the

Small intestine (duodenum)

Pancreatic juices help with

chemical digestionW

Which of the following macromolecule would have hindered digestion if a gallstone blocked the gallbladder?

Lipids

Three major reflex stages

cephalic gastric and intestinal
- initiated by parasympathetic system and regulated by hormones and reflexes of the enteric nervous system (sensitive to emotions)

Gastroduodenal reflex

neuronal circuits that stay within digestive system (no CNS)

Stomach and intestine has a complex network of neurons called

enteric nervous system (submucosal and myenteric plexus)
Afferent--> efferent paths (no interneurons)

reflexes can be initiated and or modified by the

Central nervous system

Regulation of gastric function
cephalic phase

Initiation of reflex (only phase requiring CNS)

Afferent input of cephalic phase

sight smell, thought of food
- sensory info integrated in the brain

efferent output:
cephalic phase

parasympathetic system stimulate the enteric nervous system via the vagus nerve
- causes secretion of gastric juices in preparation for the arrival of food

Regulation of gastric function
Gastric phase

arrival of food causes muscular reflexes and secretion of gastrin resulting in increased motility and secretion

afferent input for gastric phase

(NO CNS)
entry of food into the stomach
- rugae will stretch
- mechanoreceptors (afferent neurons of reflex) are in the muscular walls of stomach,

As food enters the stomach the mechanoreceptors will ______ the rate action potentials to efferent neurons

increase

Efferent output of gastric phase

increased release of even more gastric secretions initiated in the cephalic stage and muscle contractions.
-positive feedback (increase in response)

Regulation of gastric function
Intestinal phase

- No CNS
-arrival of food in duodenum of small intestine triggers release of hormones that block the effect of gastrin and inhibit gastric activity.

Afferent input of intestinal phase

- food is ejected to small intestine
- mechanoreceptors sense, send action potentials to efferent neurons of enteric nervous system

Efferent output of intestinal phase

-small intestine, enteroendocrine cells secrete hormones which inhibit gastric function and/or promote accessory organs

What event will occur immediately after mechanoreceptors are activated (send action potentials) in the stomach?

Gastrin releasee will increase

what event will occur immediately after mechanoreceptors are activated (send action potentials) in the small intestines?

GIP will be secreted (to inhibit to stomach)
-parietal cell function will decrease
- pancreatic secretions will increase

The small intestine- jejunum and illeum role

rest of small intestine (ileum and jejunum) has a high surface area for absorption of nutrient

_____ and ______ help improve the surface area for absorption of nutrients

villi and microvilli

Mucosa layer of jejunum and ileum consist of..

absorptive epithelium
- simple columnar
-mucous producing cells

Blood inn the vessel going to the liver is nutrient ___ and oxygen ____

rich and poor

steps of where absorbed nutrients go?

- Nutrients absorbed by cells of villi
- enter blood stream at capillary in villi then collected by vein
- goes to liver via the hepatic portal system
- liver helps remove absorbed nutrients from blood and further metabolizes the nutrients.

The large intestine functions in

reabsorption of water and salts resulting in feces.

four regions of large intestine

-ascending (incl cecum and appendix)
-transverse
-descending
-sigmoid

Longitudinal muscularis is modified to form ______ that results in pockets called ____

tenia coli
haustrum ( specialized muscularis layer, 3 strands tenia coli give colon pouches