Topic 14 Homeostasis. Flashcards
Describe the concept of homeostasis in mammals.
Homeostasis refers to the maintenance of a constant internal environment within an organism, crucial for optimal cellular function.
In mammals, this involves regulating core temperature, blood glucose concentration, and blood water potential within narrow limits.
The immediate environment of cells, primarily the tissue fluid, must remain stable in composition, pH, and temperature to ensure metabolic processes operate efficiently. Deviations can lead to impaired cellular function.
Explain the importance of temperature regulation in homeostasis.
Temperature regulation is vital for homeostasis as it directly affects metabolic reactions within cells.
At low temperatures, metabolic processes slow down, potentially leading to insufficient energy production.
Conversely, high temperatures can denature proteins, including enzymes, disrupting their function.
Thus, maintaining a stable core body temperature is essential for sustaining life and ensuring that biochemical reactions proceed at optimal rates.
How does water potential influence cellular function in mammals?
Water potential is a critical factor in homeostasis, affecting the movement of water in and out of cells.
An increase in water potential can cause cells to swell and potentially burst, while a decrease can lead to water leaving the cells, which results in the cell shrinking (crenating).
Define negative feedback mechanisms in the context of homeostasis.
Negative feedback mechanisms are regulatory mechanisms where a change in a variable triggers a response that opposes the initial change, thus stabilizing the system and maintaining a constant internal environment.
When a receptor detects a stimulus, such as a change in blood temperature or water potential, it sends this information to a control center in the brain or spinal cord.
The control center then signals effectors, like muscles or glands, to initiate a response that counteracts the initial change, restoring balance and stability to the internal environment.
List and explain some physiological factors controlled by homeostasis in mammals.
Homeostasis in mammals regulates several physiological factors to maintain internal stability. These include:
- Core body temperature which ensures optimal enzyme activity,
- Concentration of metabolic waste substances like CO₂ and urea which must be kept low to prevent toxicity,
- Blood pH which is crucial for enzyme function,
- Water potential of blood, affecting cell hydration,
- Concentrations of respiratory gases (O₂ and CO₂), which are vital for respiration and energy production.
Define osmoregulation and its importance in the body.
Osmoregulation is the process by which an organism regulates the osmotic pressure of its body fluids to maintain homeostasis.
This is crucial for ensuring that cells function optimally, as imbalances can lead to dehydration or overhydration.
Osmoreceptors detect changes in osmotic pressure, and the kidneys play a key role in regulating fluid balance by adjusting the concentration of urine.
Proper osmoregulation is vital for maintaining blood pressure, nutrient transport, and overall cellular health.
Do the endocrine and nervous systems work together in homeostasis?
Yes, the endocrine and nervous systems collaborate closely to maintain homeostasis in the body.
The nervous system provides rapid responses to changes in the environment through electrical signals, while the endocrine system uses hormones for longer-lasting effects.
Describe the main nitrogenous excretory products in humans.
Humans primarily excrete three nitrogenous products: urea, creatinine, and uric acid.
Urea is the main product formed from the breakdown of proteins and amino acids, serving as a key waste product in urine.
Creatinine is produced from creatine, which is synthesized in the liver and used in muscles for energy storage; some creatine is converted to creatinine and excreted.
Uric acid results from the breakdown of purines found in nucleotides and is also excreted in urine.
Explain the structure and function of the kidneys in the human body.
The kidneys are vital organs located in the lower back region, responsible for filtering blood and removing waste products.
Each kidney receives blood through a renal artery and returns it via a renal vein.
They regulate blood’s water potential and produce urine, which is transported to the bladder via the ureter.
The kidneys consist of three main areas: the cortex, medulla, and pelvis, and are composed of thousands of nephrons, the functional units that perform filtration and reabsorption.
Define the structure of a nephron and its components.
A nephron is the functional unit of the kidney, consisting of a renal tubule and associated blood vessels.
It begins with the Bowman’s capsule, which encases a glomerulus, a network of capillaries where filtration occurs.
The nephron then extends into the proximal convoluted tubule, followed by the loop of Henle in the medulla, and returns to the cortex via the distal convoluted tubule.
Finally, it connects to the collecting duct, which channels urine into the pelvis for excretion.
How does the kidney regulate water potential in the blood?
The kidneys regulate blood water potential through a process of filtration, reabsorption, and secretion.
They filter blood in the glomerulus, allowing water, ions, and small molecules to pass into the nephron while retaining larger molecules and cells.
As the filtrate moves through the nephron, water and essential solutes are reabsorbed back into the bloodstream, adjusting the concentration of urine.
Hormones like antidiuretic hormone (ADH) further influence water reabsorption in the collecting ducts, ensuring homeostasis.
Do kidneys have a protective structure, and what is its significance?
Yes, the kidneys are encased in a tough outer capsule that provides protection against physical damage and infection.
This fibrous capsule helps maintain the shape of the kidney and serves as a barrier to pathogens.
Additionally, the capsule plays a role in anchoring the kidneys in place within the abdominal cavity, ensuring they remain properly positioned to function effectively in filtering blood and producing urine.
Explain the pathway of urine from the kidneys to excretion.
Urine formation begins in the nephrons of the kidneys, where blood is filtered and waste products are collected.
Once formed, urine flows from the nephrons into the collecting ducts, which converge and lead to the renal pelvis.
From the renal pelvis, urine travels down the ureters, muscular tubes that transport it to the bladder for storage.
When the bladder fills, urine is expelled from the body through the urethra, completing the excretory pathway.
Describe the role of the afferent and efferent arterioles in the kidney’s glomerulus.
The afferent arteriole is a branch of the renal artery that supplies blood to each glomerulus, allowing for the filtration of blood.
Once the blood is filtered, the capillaries of the glomerulus converge to form the efferent arteriole, which carries the filtered blood away from the glomerulus.
This efferent arteriole then connects to a branch of the renal vein, ensuring that the filtered blood is returned to the circulatory system after passing through another network of capillaries.
The afferent arteriole has a larger diameter than the efferent arteriole, creating high glomerular pressure for filtration. This forces water, ions, and small molecules into the Bowman’s capsule.
Explain the process of ultrafiltration in the nephron.
Ultrafiltration is the first stage of urine formation in the nephron, occurring in the glomerular capsule.
It involves the filtration of small molecules such as water, glucose, amino acids, salts, and urea from the blood into the tubular fluid.
This process is driven by high hydrostatic pressure in the glomerular capillaries, forcing these small molecules through the capillary endothelium, the basement membrane, and the podocytes of Bowman’s capsule, which have tiny gaps that facilitate filtration.
Define the structure and function of podocytes in the nephron.
Podocytes are specialized epithelial cells that line the inner surface of Bowman’s capsule in the nephron.
They have finger-like projections that interdigitate, creating filtration slits. These slits allow for the selective passage of small molecules while preventing larger molecules, such as proteins, from entering the tubular fluid.
How does the basement membrane contribute to the filtration process in the kidney?
The basement membrane in the kidney act as a selective barrier between the blood in the glomerular capillaries and the lumen of Bowman’s capsule.
Composed of a network of collagen and glycoproteins, it provides structural support while also filtering out larger molecules and proteins from the blood.
This selective permeability is essential for maintaining the composition of the filtrate and ensuring that only small molecules pass through during ultrafiltration.
Do the stages of urine formation in the nephron include selective reabsorption?
Yes, the stages of urine formation in the nephron include selective reabsorption, which follows ultrafiltration.
After the initial filtration of small molecules into the tubular fluid, the nephron selectively reabsorbs essential substances such as glucose, amino acids, and certain ions back into the bloodstream.
This process occurs primarily in the proximal convoluted tubule and is vital for conserving valuable nutrients and maintaining the body’s electrolyte balance, ultimately leading to the formation of concentrated urine.
Define selective reabsorption in the context of kidney function.
Selective reabsorption is where useful substances are reabsorbed from the nephron fluid back into the bloodstream.
This process primarily occurs in the proximal convoluted tubule, where essential molecules such as glucose, vitamins, water, inorganic ions (like Na+ and Cl-), and amino acids are reabsorbed.
This mechanism ensures that the body retains necessary nutrients while allowing waste products to be excreted, maintaining homeostasis.
How does the structure of the proximal convoluted tubule facilitate reabsorption?
The proximal convoluted tubule is lined with a single layer of cuboidal epithelial cells, which are specially adapted for reabsorption.
These cells feature microvilli that significantly increase the surface area for absorption, allowing for more efficient uptake of nutrients and water.
Additionally, the presence of various transport proteins and channels in the cell membranes aids in the selective reabsorption of glucose, amino acids, and ions, ensuring that essential substances are efficiently reabsorbed from the filtrate.
Explain the role of solute concentration in the glomerular filtration process.
Solute concentration plays a critical role in the glomerular filtration process by affecting water potential.
In the glomerular capillaries, the solute concentration is typically higher than in the Bowman’s capsule, resulting in a lower water potential in the blood plasma.
This difference in water potential is significant because it drives water to move from the area of higher water potential (the blood) to the area of lower water potential (the Bowman’s capsule), facilitating the formation of filtrate.
Describe the process of re-absorption in the proximal convoluted tubule.
Re-absorption in the proximal convoluted tubule begins with Na+/K+ pumps in the basal membranes of the tubule cells, which actively transport Na+ out of the cell into the blood using ATP made by mitochondria.
The basal membrane is folded to give a large surface area for many of these carrier proteins.
This action lowers the intracellular Na+ ion concentration in the cytoplasm, prompting Na+ to diffuse from the tubular fluid into the cells via co-transporters proteins.
This passive movement of Na+ provides the energy needed to transport glucose against its concentration gradient.
Once inside, glucose diffuses into the blood through GLUT proteins. The removal of solutes raises the water potential of the filtrate, creating a gradient that facilitates water reabsorption.
Explain the role of the loop of Henle in kidney function.
The loop of Henle plays a crucial role in kidney function by establishing a high concentration gradient of Na+ and Cl- in the medullary tissue fluid.
This gradient is essential for the reabsorption of water from the collecting duct as it passes through the medulla.
The loop consists of a descending limb, which is permeable to water, and an ascending limb, which actively transports Na+ and Cl- out but is impermeable to water.
This mechanism allows for the creating the osmotic gradient necessary for water reabsorption in the collecting duct, ultimately aiding in urine concentration, conserving water in the body and preventing dehydration.
Explain the role of the distal convoluted tubule in urine formation.
The distal convoluted tubule (DCT) plays a crucial role in urine formation by reabsorbing ions and water.
The first part of the DCT actively pumps Na+ ions into the tissue fluid, while K+ ions are transported into the tubule.
The second part of the DCT is where water moves out into the medulla due to a low water potential created by the loop of Henle, leading to concentrated urine that eventually flows into the ureter.
