Digestive System Flashcards
What are the types of Digestion? And what are the types of complex organic molecules from food?
- Mechanical
- physical breaking up of food
-> in order to expose more surface area for action of digestive enzymes - Chemical
- action of digestive enzymes
- complex chemical molecules converted into simpler chemicals the body can use
3 types of complex organic molecules from food
1. Protein
2. Carbohydrates
3. Fats
What happens in the Oral Cavity?
Initiation phase of mechanical breakdown of food
- Mastication (chewing)
- Tongue keeps food btwn teeth and mixes food with saliva (increases efficiency of chewing)
Initial chemical digestion
- Salivary amylase: starts chemical breakdown of carbohydrates
What do the Salivary Glands do?
Types: parotid, submandibular, and sublingual
Saliva is made from blood plasma
- Contains lysozymes which inhibit bacterial growth
Secretion of salivary glands is continuous, but amount depends on ANS
What is the Pharynx and what does it do? And what does the medulla coordinate?
Channel for swallowing
-> Constrictor muscles of pharynx contract reflexively when tongue pushes food backward
Located in MEDULLA: reflex center for swallowing
Coordinates:
- Constriction of pharynx
- Cessation of breathing
- Elevation of soft palate to block the nasopharynx
- Elevation of larynx and closure of epiglottis
- Peristalsis of esophagus
Describe the esophagus and what it is made of.
Connects pharynx to stomach
MADE OF SMOOTH MUSCLE
- Peristalsis moves food down esophagus
Lower esophageal sphincter: non-volitional, smooth muscle
- Relaxes to allow food to enter stomach
- Constricts to prevent backflow of stomach contents
What happens and what is contained in the Mucosa Layer?
Contains…
Epithelial Tissue
-> Secretes mucous to lubricate for food passage
-> In the stomach and small intestine: release digestive enzymes
Areolar CT
-> Contains lymph nodules and macrophages
Smooth muscle
-> Creates folds in mucosa to INCREASES SURFACE AREA in stomach and small intestines
What happens and what is contained in the Submucosa layer?
Contains…
- Areolar CT
- Blood and lymphatic vessels
-
Meissner’s Plexus (submucosal plexus)
-> Innervates mucosa to REGULATE SECRETIONS - Sensory neurons from smooth muscle
- Motor neurons to blood vessels
-> Regulate vessel diameter (vasoconstriction and vasodilation) and blood flow
What happens and what is in the External muscle layer?
- Contractions break up food and mix it w/ digestive enzymes and secretions
- One-way contractions of peristalsis moves food down food through tube
Auerbach’s plexus (mysenteric plexus)
-> portion of ENS
-> Receive autonomic impulses that regulate contractions (regulates peristalsis)
What is the Serosa and what is in it?
- Fibrous connective tissue in structures above diaphragm
-> Esophagus
Mesentery or visceral peritoneum in structures below diaphragm
-> Serous membrane
protective layer holds viscera in place, adds stability when moving around
fluid layer reduces friction between viscera
Where does most digestion in the stomach take place?
Pylorus
What is rugae in the stomach?
Mucosa in the stomach is wrinkled or folded (rugae) when stomach is EMPTY
-> flattens out as stomach is filled and permits expansion w/out tearing
What are the different types of cells in the stomach?
Gastric juice: collective secretions of the stomach
-> Produced by various cells w/in “gastric pits” of stomach
- Mucous cells: secrete mucous
-> coats lining to help prevent erosion by the acidic gastric juice - Chief cells: secretes pepsinogen (inactive form of pepsin)
- Parietal cells: produce hydrochloric acid (HCl) and secrete intrinsic factor
-> HCl: makes gastric juice very acidic (pH 1-2) which kills microorganisms in stomach
-> Converts pepsinogen to pepsin
- Pepsin begins digestion of proteins
-> Intrinsic factor: essential for absorption of vitamin B12 in ileum - G cells: secrete the hormone Gastrin
-> Gastrin: stimulates secretion of greater amounts of gastric juice
What is the stomach’s pyloric sphincter?
Pyloric sphincter is contracted as stomach churns food
- Relaxes at intervals to allow small amounts of chyme to enter duodenum
- Contracts again to prevent backflow of intestinal contents into stomach
What happens in the small intestines?
Digestion is completed in small intestine
-> major site for nutrient absorption (villi and microvilli increase surface area for absorption)
w/in each villi is a capillary network and lacteal (lymphatic vessel)
-> Absorption of nutrients takes place from INTESTINE INTO VESSELS w/in villi
What is in the mucosa of the small intestines?
Mucosa: simple columnar epithelium cells with microvilli
-> Goblet cells secrete mucous
-> Enteroendocrine cells secrete hormones, which is stimulated by food entering duodenum
-> Peyer’s patches (lymph nodules)
How are molecules absorbed in the small intestines?
Water-soluble nutrients are absorbed into blood in capillary networks
Active transport: Monosaccharides, amino acids, POSITIVE IONS (+), and water soluble vitamins
Passive or active transport: NEGATIVE (-) IONS
Osmosis: water absorbed following absorption of minerals, especially Na
Additional substances for absorption
- Intrinsic factor: needed for Vitamin B12 absorption
- Parathyroid hormone and vitamin D: needed for Ca absorption
Where does blood from the villi travel to from the capillaries?
Blood passes though portal vein to the liver before going to the heart
Enables liver to…
- Regulate blood levels of glucose and amino acids
- Store certain vitamins
- Remove potential toxins from blood
How is fat absorbed in the small intestines?
Fat-soluble nutrients is absorbed into the lymph via lacteals
- Bile salts are needed for efficient absorption of fatty acids and fat soluble vitamins (A,D,E,K)
-> Once absorbed, fatty acids are recombined with glycerol to form triglycerides
-> Triglycerides form globules that include cholesterol and protein -> chylomicrons
-> Most absorbed fat is transported in form of chylomicrons by lymph and eventually enters the blood
Characteristics of the Liver
“Metabolic factory” of the body
Liver Lobule: structural unit of the liver
Hepatocytes: column of liver cells
-> Store nutrients
- Play role in carbohydrate, protein, fat metabolism
What are sinusoids?
Capillaries of a lobule
- Very permeable vessels b/w hepatocytes
- Receive blood from both hepatic artery and portal vein
-> Hepatic artery: brings oxygenated blood
-> Portal vein: brings blood from digestive organs and spleen
Each lobule has a central vein
- Central veins unite to form hepatic veins
-> bring blood out of liver to IVC
What is the liver’s only digestive function?
Production of bile
Bile
- Mostly water
- Carries bilirubin and excess cholesterol to intestines to be eliminated
- Digestive function: bile sals emulsify fats in small intestine
Secretin: hormone that stimulates bile production
-> produced by duodenum when food enters small intestines
What are the liver’s no digestive functions?
- Carbohydrate metabolism -> regulation of blood glucose level
- A.a. Metabolism -> regulates blood levels for a.a. For protein synthesis
- Lipid metabolism -> forms lipoproteins for transport of fats in blood
-> synthesizes cholesterol and excretes excess into bile - Stores…
-> Vitamins A,D,E,K, and B12
-> Iron
-> Copper - Plasma protein synthesis
- Production of clotting factors
- Phagocytosis
-> Breaks down old RBCs
-> engulfs pathogens - Bilirubin formation
- Detoxification
-> produces enzymes to neutralize substances such as medications, alcohol, ammonia
What does the gallbladder do?
Functions to concentrate and store bile
- Choleocystokinin: secreted by duodenal cells when fatty foods enter duodenum
-> stimulates contraction of the gallbladder
-> forces bile into cystic duct -> common bile duct -> duodenum
What are the pancreas’ exocrine functions?
Produces digestive enzymes for breakdown of carbs, proteins, and fats
What are the digestive enzymes produced by the pancreas and what do they do?
Pancreatic amylase: digests starch
Lipase: converts emulsified fats to fatty acids and glycerol
Trypsinogen: inactive enzyme that converts to active trypsin in duodenum
-> trypsin: digests polypeptides to shorter chains of amino acids
What is pancreatic enzyme juice?
Carried to duodenum via main pancreatic duct (joining common bile duct)
bicarbonate juice (alkaline) to neutralize the gastric juice entering the duodenum
- Secretin and cholecystokinin stimulate secretion of pancreatic juices
-> Secretin: stimulates production of bicarbonate juice
-> Cholecystokinin stimulates secretion of pancreatic enzymes
What does amylase do and where is it secreted and site of action?
Function: Carbohydrate digestion
Secreted by: Salivary glands
Site of action: Oral Cavity
What does Pepsin and HCl do and where are they secreted and site of action?
Function
Pepsin: protein digestion
HCl: converts pepsinogen to pepsin; maintains pH of stomach; destroys pathogens
Secreted by: Stomach
Site of Action: Stomach
What do bile salts do and where is it secreted and site of action?
Function: Fat digestion
Secreted by: liver
Site of Action: Small Intestine
What does Amylase, Trypsin, and Lipase do and where are they secreted and site of action?
Function
Amylase: Carbohydrate digestion
Trypsin: Protein digestion
Lipase: Fat digestion
Secreted by: Pancreas
Site of Action: Small Intestine
What does peptidases, sucrose, Maltase, and lactase do and where are they secreted and site of action?
Function
Peptidases: Protein digestion
Sucrose: Carbohydrate digestion
Maltase: Carbohydrate digestion
Lactase: Carbohydrate digestion
Secreted by: Small Intestine
Site of Action: Small Intestine
What is the Large Intestines (Colon) made of ?
Extends from ileum to small intestine to anus
- Cecum
- Ileocecal valve: fold of intestinal mucosa surrounding opening from ileum to cecum
-> Prevents backflow of fecal material into small intestine - Ascending colon 3. Transverse colon 4. Descending colon (encircle small intestine)
- Sigmoid colon
- Rectum
- Anal canal
What happens in the large intestines?
No digestion takes place here
Colonic mucosa: secretes mucus to lubricate the passage of fecal material
Functions
- Absorption of water, minerals, and vitamins
-> ~80% of water that enters the colon is absorbed
-> Positive and negative ions are absorbed
-> Vitamins produced by the normal flora
- Elimination of undigestible material
Everything absorbed by colon circulates first to the liver by way of portal circulation
What is feces and what are the different reflexes?
- Cellulose and other undigesetible material, dead and living bateria, and water *
Colon moves feces along via peristalsis
- Gastrocolic reflex: presence of food in stomach and peristalsis causes colon to contract
- Duodenocolic reflex: presence of chyme and peristalsis of duodenum causes colon to contract
- Defecation reflex: spinal cord reflex that can be controlled volitionally
-> stretching in the wall of the rectum by the entry of feces stimulates reflex (smooth muscles of rectum contract)
-> Internal anal sphincter relaxes, PERMITTING defecation
- External anal sphincter: skeletal muscle under volitional control
-> can be contracted to PREVENT defecation
