To see the answer, click on the flashcard. Use the arrow keys on your computer or the arrow buttons below to flip through the questions. If you want to review the MCAT content covered in this flashcard deck, keep reading below for a summary of homeostsis.
Each flashcard is bring you closer to your target score!
Front of the card
Back of the card
Homeostasis is the body's ability to maintain a stable internal environment despite changes in external conditions. Key systems involved in homeostasis include the excretory system, the skin, and hormonal regulation.
The excretory system, primarily consisting of the kidneys, ureters, bladder, and urethra, plays a crucial role in maintaining homeostasis by regulating the composition of blood and bodily fluids. The kidneys perform several essential functions: filtration, secretion, and reabsorption. The nephron, the functional unit of the kidney, filters blood to form urine. The renal vascular pathway starts from the renal artery, proceeds to the afferent arteriole, glomerulus, efferent arteriole, vasa recta, and ends at the renal vein.
Filtration occurs in the glomerulus, where approximately 20% of the blood passing through is filtered into Bowman's space. If blood cells or proteins are found in urine, it indicates a problem with the glomerulus. The filtrate then enters the proximal convoluted tubule (PCT), where essential nutrients such as amino acids, glucose, water-soluble vitamins, and salts are reabsorbed. Waste products like hydrogen ions, potassium ions, ammonia, and urea are secreted into the PCT.
The loop of Henle, distal convoluted tubule, and collecting duct further refine the filtrate by reabsorbing water and salts as needed. The final concentration of urine depends on the permeability of the collecting duct, which is regulated by hormones like antidiuretic hormone (ADH) and aldosterone. ADH lowers blood osmolarity by increasing water reabsorption, while aldosterone promotes the reabsorption of salt and water without changing blood osmolarity.
When blood pH is too high, the kidneys excrete more bicarbonate and increase the reabsorption of hydrogen ions. Conversely, when blood pH is too low, they excrete more hydrogen ions and reabsorb more bicarbonate. This regulation ensures the blood maintains an optimal pH balance.
The skin is the largest organ and a vital component of homeostasis, acting as a barrier and regulating body temperature and fluid balance. The skin has three main layers: the hypodermis (subcutaneous layer), dermis, and epidermis.
The epidermis is subdivided into five layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. The stratum basale contains stem cells responsible for producing keratinocytes, while melanocytes, derived from neural crest cells, produce melanin, the pigment responsible for skin color. Langerhans cells, found in the stratum spinosum, are special macrophages that present antigens to T-cells, activating the immune system.
Keratinocytes in the stratum granulosum die and lose their nuclei, forming a tough, protective layer. The stratum lucidum is present only in thick, hairless skin such as the palms and soles. The outermost layer, the stratum corneum, consists of several dozen layers of flattened keratinocytes that prevent pathogen invasion and fluid loss.
The dermis houses sweat glands, blood vessels, hair follicles, and most sensory receptors. Sweat glands are controlled by the autonomic nervous system and play a crucial role in thermoregulation by facilitating heat loss through evaporation.
Several hormones regulate homeostasis. ADH and aldosterone are crucial for maintaining fluid balance by altering the quantity of water reabsorbed in the kidneys. ADH, inhibited by substances like alcohol and caffeine, lowers blood osmolarity by increasing water reabsorption. Aldosterone, on the other hand, promotes the reabsorption of salt and water without changing blood osmolarity.
Renin, an enzyme released by the kidneys, cleaves angiotensinogen to form angiotensin I, which is then converted to angiotensin II. This sequence plays a vital role in blood pressure regulation by constricting blood vessels and stimulating aldosterone release.
Overall, homeostasis involves intricate interactions between various organs and systems, ensuring the body's internal environment remains stable and optimal for survival. Understanding these mechanisms is crucial for comprehending how the body adapts to internal and external changes.