Homeostasis Flashcards
Principles of Homeostasis
What is the definition of Homeostasis
Homeostasis is the maintenance of constant or steady state conditions within a living organism
Provide examples of factors that Homeostasis controls?
-Blood
-pH
-Temperature
-Water potential
-Salt
-Glucose
Ensures they are kept within normal limits
What type of reaction is Homeostasis and how is it controlled?
Homeostasis is a cellular biochemical reaction and is controlled by enzymes-activity is affected by fluctuating temperature and pH levels
Name the order of the Homeostatic response
- Control System (receptor)
- Co-Ordinator
- Effector
- Response
- Feedback
Explain the features of a Homeostatic response
- Control system (brain) has sensors (receptors) which monitor the factor being controlled. Receptors can be in the brain or throughout the body
- A Co-ordinator receives and controls information from the receptor and triggers a reaction to correct the change
- The CORRECTIVE MECHANISM (Effector)- brings about change- results in regulation of the factor when the receptors detect a change from normal levels (set point- optimal conditions)
- NEGATIVE FEEDBACK system stops the corrective mechanism and prevents over- correction
What type of control is the communication between the receptors and monitor and effectors
Either nervous (human body temperature) or hormonal (glucose levels)
State and explain the 2 functions of the Kidney
- Excretion- the removal of toxic waste produts of metablism, eg Nitrogen containing compounds, such as Urea, which is produced by the breakdown of excess amino acids and nucleic acids in the liver.
-Creatinine- a waste product produced from the breakdown of creatine phosphate (important in ATP synthesis) in muscles - Osmoregulation- control and maintain optimal water potential of body fluids under the influence of Antidiuretic Hormone (ADH). Kidney regulates the volume and concentration of urine produced.
Explain the structure of the Urinary (excretory system)
- Blood travels through the AORTA and RENAL ARTERY under high pressure. This is required for the filtration process.
- The kidney acts as a FILTER getting rid of excretory products and excess water and keeping useful products in the blood.
- The filtered blood then leaves via the RENAL VEIN.
- The waste products and excess water pass out via URETER as urine to the BLADDER to be stored.
- SPHINCTER MUSCLES control the release of urine as it exits via the URETHRA.
Describe the structure of the Kidney
Inside the kidney, there are 2 main layers:
-Outer CORTEX (site of filtration)- dark region
-Inner MEDULLA surrounding a central cavity, the pelvis (lighter region)
-Medulla i subdivided into PYRAMIDS
Explain the structure of the Nephron
-The nephron is the functional unit of the kidney
-There are over 1 million nephons in one kidney and each nephron acts as a filter
The nephron consists of:
*A cup shaped Bowman’s capsule:
-Blood enters each capsule through an AFFERENT ARTERIOLE (branch of the renal artery)
-This branches inside the Bowman’s capsule to form a knot of capillaries called the GLOMERULUS.
-Blood leaves here vi an EFFERENT ARTERIOLE, which branches to forma further capillary network (vasa recta system) around the main body of the Nephron.
-The Bowman’s capsule extends into a coiled tube called the PROXIMAL CONVOLUTED TUBULE (first coiled) tubule.
-This leads into a long hairpin tube called the LOOP OF HENLE (descending and ascending limb)- runs deep into the medulla of the kidney, bends and sharply returns back into the cortex where it forms another twisted region, the DISTAL CONVOLUTED TUBULE.
-Many DCTs join to form a COLLECTING DUCT, which transfers the fluid (urine) toward the pelvis of the kidney and the contents are emptied into the URETER which takes urine to the BLADDER.
State the steps involved in the production of urine
-Ultrafiltration in the bowman’s Capsule- cleaning of the blood
-Selective Reabsorption in the proximal Convoluted Tubule
Explain how the process of Ultrafiltration takes place?
Differential width of the afferent and efferent arteriole blood vessels cases a build up of hydrostatic pressure within the glomerulus. Plasma without plasma proteins are forced into the Bowman’s Capsule, through the basement membrane/ endothelium of the glomerulus contains pores/ inner wall of Bowman’s Capsule is composed of cells (podocytes) with foot-like processes and spaces between them (filtration slits).
What is the definition of Ultrafiltration
Plasma within the glomerulus is filtered into the Bowman’s Capsule under high hydrostatic pressure.
Can any products filter into the Bowman’s Capsule?
-Only small substances below a certain size (under 68000 RMM) is filtered out of the capillaries and so the filtrate contains useful molecules aswell as toxic ones.
What products can and cannot be filtered?
Can:
-Water
-Glucose
-Amino acids
-Salt (sodium and chloride)
-Urea
-Vitamins/minerals
-Small proteins
Cannot:
-Large proteins
-Blood cells
Why is Filtration driven by hydrostatic pressure?
-The renal arteries are wide, short and relatively close to the heart
-The afferent arteriole of each glomerulus is wider than the efferent arteriole.
-The coiling of the capillaries in the glomerulus further restricts blood flow, increasing pressure.
Explain the 3 layers separating the plasma from the filtrate (glomerular filtrate)
- Endothelium of the capillaries in the glomerulus- this is a single layer of squamous (flattened) endothelial cells with pores- making them more permeable
- The effective filter is the BASEMENT MEMBRANE of the glomerular capillaries. The membrane is an extracellular matrix formed from different substances including proteins- prevents large proteins and blood cells leaving the blood.
- The INNER WALL of the Bowman’s capsule sonsists of specialised cells called PODOCYTES with foot like processes which surround the capillaries but have spacious gaps between them- FILTRATION SLITS
Explain how water potential links
-water potential is another force which should be compared
-for filtration to occur, the water potential within the glomerular capillaries (blood plasma) must exceed the water potential within the Bowman’s capsule (glomerular filtrate).
What is the definition of water potential
The tendancy of water molecules to enter or leave a solution via osmosis. Water will move from an area of high water potential (less negative) to an area of lower water potential (more negative) through a selectively permeable membrane. The steeper the gradient, the greater the tendancy for water to leave
How is the difference in water potential produced
-The hydrostatic pressure of the blood is much greater than the hydrostatic pressure created by the filtrate in the nephron
-the solute potential is represented by the plasma proteins in the glomerulus, and are not found in the filtrate as they are too big. Therefore, the filtrate will have a less negative solute potential (higher water potential) that the blood in the glomerulus.
-This difference in filtration opposes filtration, however this is insignificant when compared to the different in hydrostatic pressure across the basement membrane.
-It’s the net filtration pressure that causes fluid to move from the glomerular capillaries into the Bowman’s Capsule.
How to work out Net Filtration
- Water potential is Solute Potential add Pressure Potential
- Work out the water potential of both the glomerular capillaries and the glomerular filtrate
- Take away the two answers to find out the net filtration force
Explain the result on a positive net filtration force
The water potential of the blood plasma (glomerulus) is higher that the glomerular filtrate in the Bowman’s Capsule, therefore producing the net filtration force/ pressure that forces liquids through the basement membrane.
Explain the process of Selective Reabsorption
-Some substances are reabsorbed back into the blood as the filtrate moves along the PCT.
-Some are actively reabsorbed, called selective (eg, urea, this is toxic and not actively reabsorbed, but some passes by diffusion into the blood- (below 50%)
-Glucose, salt, amino acids and some sodium and chloride ions are selectively reabsorbed into the blood by FACILITATED DIFFUSION (protein carriers) (when a gradient exists) and ACTIVE TRANSPORT (need energy-ATP)- to ensure all glucose is reabsorbed.
-small proteins are reabsorbed by PINOCYTOSIS
-Therefore, the blood in the capillaries surrounding the nephron has a HIGH SOLUTE POTENTIAL (low water potential)
-A large amount of water (70-80%) passes out of the filtrate and back into the blood by OSMOSIS- HIGH_LOW concentration
-As water is absorbed, urea concentration increases in the PCT (water is lost)
-At the end of the PCT, the filtrate is ISOTONIC with the blood in the plasma.
Explain the cells of the PCT
-epithelial cells
-have a high levels of metabolic activity
-carry out energy demanding processes
