digestion and metabolism Flashcards
LEARNING OBJECTIVES 1. List and describe the major processes occurring during digestive system activity. 2. Describe the tissue composition and the general function of each of the four layers of the alimentary canal. 3. Describe the basic functions of the mouth, pharynx and oesophagus. Include a brief description of the functions of saliva. 4. Outline the basic anatomy of the stomach, small intestine and large intestine and the digestive processes that occur in these locations. 5.
In order what are the six major processes involved in digestion?
- Ingestion
- Propulsion
- Mechanical breakdown
- Chemical digestion
- Absorption
- Defaecation
what areas of the body involve mechanical breakdown?
mouth: chewing and mixing food with saliva
stomach: churning and mixing with gastric juice
small intestine: segmentation = mixes food with digestive juices and aids in nutrient absorption
What are the names of the 4 basic layers of the alimentary canal and what are they made of?
Serosa- epithelium and connective tissue
Muscularis externa- longatudinal muscle and circular muscle
Submusosa - loose connective tissue with elastic
Mucosa- Epithelium, lamina propia and muscularis mucisae
What is the function of the Mucosa layer of the alimentary canal?
_Mucosa - The most inner laye which is made up of three subay _
- Epithelium: secretes mucus protects the mucosa, helps move food along secretes digestive enzymes chemical digestion secretes hormones control motility and secretion of digestive juices absorbs nutrients.
- Lamina propria: contains capillaries absorption of the end products of digestion, nourishes epithelium lymphoid tissue protection against bacteria and pathogens.
- Muscularis mucosa: produces folds in the mucosa of the small intestine to increase the surface area for absorption
What is the structure and function of the Submucosa layer of the alimentary canal?
Loose connective tissue with elastic tissue allows stretch and recoil
Rich supply of:
blood vessels: for nutrient absorption
lymphatic vessels: for transports lipids
lymphoid tissue: for immune function
nerves: parasympathetic –> motility and secretion
sympathetic --\> motility and secretion
What is the function of the Mucularis externa layer of the alimentary canal?
Responsible for peristalsis (propulsion) and segmentation (mechanical breakdown).
Two smooth muscle layers:
- inner circular - form sphincters act as valves to control the passage of food
- outer longitudinal
What is the function of the Serosa layer of the alimentary canal?
Connective tissue covered with a thin layer of squamous epithelium.
Functions: protection of the alimentary canal anchors the alimentary tissues within the peritoneal cavity
What are the functions of the mouth?
Digestive functions of the oral cavity (mouth):
- Ingestion
- Mastication (chewing) - mechanical breakdown
- Mixing food with saliva
- Taste sensation
- Initiating chemical digestion - amylase begins chemical digestionoof charbohydrates only
- Propulsion - swallowing food (deglutition)
Chemical digestion is initiated in the mouth. What enzymes are secereted in the mouth and what do they break down?
Amylase begins chemical digestion of charbohydrates only.
Lingual lipase- begins break down of small chain fats
Describe what happends in box A.
Glycolysis- Glucose is turned into Pyruvic Acid
What do the purple arrows signify?
Anabolic reactions
What do the blue arrows signify?
Catabolic reactions
Where abouts in the cell does stage 2 occur in the cell?
cytoplasm
Where abouts in a cell does stage 3 occur?
mitocondria
what is the name of the intermediate molecule that each of the nutrients are eventualy converted to?
They are all broken down into Acytyl Co enzyme A
What is the name of the series of reactions that occur in the green box?
The Krebs Cycle
What are the three things made by the Krebs Cycle?
Carbon dioxide
Hydrogen Ions
ATP
what happens to excess glucose in the body?
It is turned into Glycogen through the process called glycogenisis and stored as fat.
What is the process labels A?
Electron transport chain
What molecule must be removed from amino acids beofre they can be used in this series of reactions?
Ammonia
What molecules are used in energy production in most tissues excluding nervous tissue?
fatty acids
keytones
glycerol
What is the hormone that donminate stage three?
Insulin
Why does the liver have a dual blood supply?
To supply it with blooth oxygen rich blood and nutrient rich blood.
The hepatic artery supplies the liver with oxygenated blood from the lungs, and the portal vein supplies it with nutrient-rich blood from the intestines.
The liver has two routes of blood supply. Which vessel supplirs blood from the small intestine and which supplies blood from the systemic circulation? And which percentage comes from each vessel?
Systemic circulation- Hepatic artery
Small intestine- Hepatic portal vein
The liver plays a vital role in stabilising blood glucose leves around 5mmol/L. What three processes occur in the liver to maintain glucose homeostasis and when so these precesses take place (eg glucose too high or too low).
- Glycogenisis - too much glucose in blood steam
- Glycogenalysis - not enough glucose in blood stream
- Gluconeogenisis - not enough glucose in blood steam = make glucose from non-glucose stores
What are the names of the three glands the mouth?
What are the functions of the stomach?
- Mechanical breakdown – mixing food with gastric juice (i.e. liquefaction of food chyme)
- Chemical digestion (proteins)
- Absorption (fat-soluble substances ONLY, e.g. alcohol)
- Storage of food
- Propulsion – to the small intestine
- Secretion of Intrinsic factor <— only essential function of the stomach
What is the empty and full volume of the stomach?
50ml empty
4L when full
what are the internal folds of the stomach lining called?
Rugae
Describe the structure and function of the muscularis externa (modified) of the stomach.
Structure- circular & longitudinal Function- mix, churn and propel food and the oblique muscle pummels the food and rams it into the small intestine
What is the structure and finction of the stomach muscosa.
This includes the types of cells and what they produce
Structurte of mucosa- lining of simple columnar epithelium that produces an alkaline mucous, dotted with: gastric pits that contain mucous cells
These gastric glands produce 3L of
gastric juice per day,
These glands include:
chief cells – secrete pepsinogen
parietal cells – secrete HCl
enteroendocrine cells – secrete hormones that control gut motility and secretion
Which cells produce pepsinogen and which cells produce HCl? Where are these cells found?
chief cells – secrete pepsinogen
parietal cells – secrete HCl
Found in the stomach
Gastric juice creates a harsh environment HCl is corrosive. Protein digesting enzymes (proteases) can digest the stomach wall. For this reason the body has a three layered mucosal barrier. What are the three layers?
- bicarbonate-rich fluid under an insoluble mucus on the stomach wall. Bicarbonate-ion rich musus nutralises acid that might get through the insoluble alkaline mucus.
- mucosal epithelial cells joined by tight junctions
- damaged mucosal epithelial cells shed and quickly replaced
What happeneds then the mucosal layer of the stomach is broken?
Leads to gastritis. Persistant damage leads to a gastic ulcer.
what is the basic structure and function of the small intestines?
To absorb as much nutrience as possible we want to have as much sueface area as possible.
what are the tree sections of the small intestine?
Duodenum
Jejunum
Ilium
Which section of the small intestine recieves bile and pancreatic juices?
Duodenum
Which section of the small intestine is the major site of chemical and mechanical degestion as well as absorption?
Jejunum
How is the small intestine adapted for nutrient absorption?
- length
- mucosa/submucosa
- circular folds
- villi
- microvilli
What is the function of the circular folds in the sall intestine?
To slow the movement of chyme and thus increasing the time for nutirent absoption
What do the micovilli of the small intestines do?
Very small, densely packed villi on the surface of
individual absorptive epithelial cells form the “brush
border”
Plasma membrane bears enzymes that complete
carbohydrate, protein and nucleic acid digestion(brush
border enzymes)
What is the function of the villi in the small intestines?
nutrient and electrolyte absorption - epithelial columnar cells, core contains a capillary bed a
produce mucous - goblet cells
What are intestinal crypts?
Intestinal crypts are are tubular glands locared in pits between villi. They secrete slightly alkaline intestinal juice that facilitates nutrient absorption.
Enteroendocrine cells produce hormones that simulate the secretion of bile and pancreatic juice.
what percentage of nutrienet absorption occurs in the small intestine?
90%
as chyme is passed from the stomach into the small intestine what stops the stomach acids from eating away at the walls of the intestines?
alkline intestinal mucus ans pancreatic juices help nutralise acidic chyme