6: Human physiology Flashcards
(47 cards)
What is peristalsis?
A wave of contraction and relaxation of the longitudinal and circular muscles of the alimentary canal, by which the contents are forced along the tube.
How do the longitudinal muscles and circular muscles work?
Antagonistically
Explain why digestion of large food molecules is essential.
- Many molecules are too large to be absorbed by the villi
- Large food molecules are broken down so they can be reorganised
Discuss the roles of the enzymes secreted by the pancreas during digestion.
- amylase breaks down starch to maltose
- lipase breaks down fats to fatty acids and glycerol
- Proteases break down proteins into smaller polypeptides
Describe the digestion of food in the human digestive system.
- Chewing food makes smaller particles of food
- Starch digestion begins in the mouth
- Digestion of proteins in the stomach
- Acid condition in stomach provides optimum pH for enzymes
- Stomach muscle contraction causes mechanical digestion
- Duodenum neutralises pH
- Enzymes in small intestine complete digestion
- Alkaline condition in small intestine provides optimum pH for enzymes
- Bile salts help to emulsify fats
- Amylase breaks down starch to maltose
Which enzymes does the pancreas secrete into the small intestine?
amylase, lipase and protease
How can the small intestine be divided?
- Serosa (outer layer)
- Longitudinal muscles
- Circular muscles
- Submucosa (connective tissue that has large veins and arteries)
- Mucosa (innermost layer)
- Mucosa consists of epithelium and villus
How are peptides digested?
Endopeptidases break proteins down into small peptides, then exopeptidases break the small piptides into amino acids, which are absorbed
Where does the absorption of food molecules take place?
In the small intestine, across the epithelium
How is the SA of the small intestine increased and why?
Villi, to ensure a large enough SA for transport proteins to absorb all necessary nutrients
What are the structures of a villi?
Outside to inside:
- Goblet cells
- Epithelium
- Lamina propria
- Capillary network
- Nerve
- Lacteal
- Venule
- Arteriole
- Lymphatic vessel
What is absorption?
the taking in of digested food substances as well as minerals and vitamins from the lumen of the small intestine into the blood.
Explain how the structure of the villus is adapted for absorption.
- Shape of villus has large SA to improve absorption
- Thin walls allow fast diffusion
- Capillaries to absord digested food products
- Lacteal in villus to absorb fatty acids
- Protein pumps in membrane to carry on active transport
- large number of mitochondria provide ATP for active transport
Explain how the structure of the villus is adapted for absorption.
- Shape of villus has large SA to improve absorption
- Thin walls allow fast diffusion
- Capillaries to absord digested food products
- Lacteal in villus to absorb fatty acids
- Protein pumps in membrane to carry on active transport
- large number of mitochondria provide ATP for active transport
What is assimilation?
The use of molecules resulting from digestion. End products of digestion are distributed around the body through the circulatory system and are used by cells for anabolic processes or for respiration.
Two-step process of absorption
- Substances to be absorbed move from the lumen into the epithelial villi
- Amino acids and monosaccharides move from the villi into the capillaries and monoglycerides move into the lacteals
Methods of absorption
simple diffusion, facilitated diffusion, active transport, and pinocytosis
Simple diffusion (in terms of absorption)
Occurs when molecules are small and are hydrophobic (so they can pass through the phospholipid bilayers). This occurs mostly with the products of lipid digestion.
Facilitated diffusion (in terms of absorption)
Fructose, glucose and other hydrophilic monomers are moved by protein channels. Be aware, this still requires a concentration gradient.
Active transport (in terms of absorption)
Is needed when the concentrations are lower in the lumen of the small intestine. Thus, the movement needs to occur against a concentration gradient. Glucose, amino acids and some mineral ions are transported in this way, which requires ATP. The cells of the epithelium have many mitochondria that can synthesise ATP for this process.
Pinocytosis (in terms of absorption)
Draws in small droplets of liquid surrounded by a small section of the phospholipid membrane. This is most likely to occur with fat droplets in the lumen of the small intestine.
How can the absorption of nutrients from the lumen of the small intestine be described?
Nutrients move from the lumen, across a plasma membrane into the epithelial cell, and across the plasma membrane again out of the epithelial cell and then into the capillary.
How is starch broken down?
- Begins with amylase in the saliva
- Breaks down bonds in amylose and amylopectin
- Still too large to pass through membranes
- Immobilised enzymes in the epithelial cells of the small intestine break down the rest
- Transported to the liver where it enters the general circulation
What is dialysis?
the separation of smaller molecules from larger molecules in solution by selective diffusion through a partially permeable (also known as selectively permeable or semipermeable) membrane.
