Biology: Chapter 10 Flashcards
The excretory system
kidneys, ureters, bladder, and urethra
Functional unit of the kidney
nephron
Path of filtrate/urine
-nephron
-renal pelvis
-ureter
-bladder
-urethra
Distinct areas of nephron tubule (in order)
-proximal convoluted tubule
-descending and ascending limbs of the loop of Henle
-distal convoluted tubule
-collecting duct
Internal urethral sphincter
consists of smooth muscle (under involuntary control) and is contracted in its normal state
External urethral sphincter
consists of skeletal muscle and is under voluntary control
Osmoregulation
-The kidney filters the blood to form urine
-Primary job of the kidneys is to regulate blood volume and osmolarity
-Kidney function may be divided into three different processes in order to achieve this: filtration, secretion, and reabsorption
Filtration (osmoregulation)
-About 20% of the blood that passes through the glomerulus is filtered as fluid into Bowman’s space; collected fluid is known as filtrate and movement is governed by Starling forces
-Hydrostatic pressure in the glomerulus is significantly higher than that in Bowman’s space which causes fluid to move into the nephron
-Osmolarity of blood is higher than that of Bowman’s space, resulting in pressure opposing the movement of fluid into the nephron
-Under most circumstances, fluid will flow from the glomerulus into Bowman’s space
-Movement of solutes from blood to filtrate at Bowman’s capsule
Secretion (osmoregulation)
-Nephrons are also able to secrete salts, acids, bases, and urea directly into the tubule by either active or passive transport
-The kidneys are capable of eliminating ions or other substances when present in relative excess in the blood
-Secretion is also a mechanism for excreting wastes that are simply too large to pass through glomerular pores
-Movement of solutes from blood to filtrate anywhere besides Bowman’s capsule
Reabsorption (osmoregulation)
-Some compounds that are filtered or secreted may be taken back up for use
-Examples include glucose, amino acids, and vitamins
-Movement of solutes from filtrate to blood
Nephron function
-keep what they body needs and lose what it doesn’t, and concentrate the urine to conserve water
-Anything that makes it into the filtrate and that is not reabsorbed will be lost from the body in urine
Proximal convoluted tubule (PCT)
-Filtrate first enters here
-Amino acids, glucose, water-soluble vitamins, and the majority of salts are reabsorbed along with water here
-Site of secretion for a number of waste products: hydrogen ions, potassium ions, ammonia, and urea; dump the HUNK (H+, Urea, NH3, K+)
Loop of Henle
-Filtrate then enters the descending limb of the loop of Henle; dives deep into the medulla before turning around to become the ascending limb of the loop of Henle
-The vasa recta and nephron create a countercurrent multiplier system meaning that the flow of filtrate through the loop of Henle is in the opposite direction from the flow of blood through the vasa recta
-The loop of Henle becomes thicker because the cells lining the tube are larger in order to allow the reabsorption of sodium and chloride by active transport
Descending limb (loop of Henle)
permeable only to water; as the descending limb travels deeper into the medulla, the increasing interstitial concentration favors the outflow of water from the descending limb, which is reabsorbed into the vasa recta
Ascending limb (loop of Henle)
only permeable to salts and is impermeable to water
Distal convoluted tubule (DCT)
-Responds to aldosterone, which promotes sodium reabsorption
-Water will follow the sodium, concentration the urine and decreasing its volume
-Anything that is not reabsorbed from the tubule by the end of the collecting duct will be excreted
How blood pressure impacts the excretory system
-decreased blood pressure stimulates release of renin from juxtaglomerular cells in the kidney
-Renin cleaves angiotensinogen, a liver protein, to form angiotensin I. This peptide is metabolized by angiotensin-converting enzymes in the lungs to form angiotensin II, which promotes the release of aldosterone from the adrenal cortex
-Aldosterone alters the ability of DCT and collecting duct to reabsorb sodium and reabsorbing more sodium allows water to flow with it which increases blood volume and blood pressure
-ADH only governs water reabsorption and thus results in a lower blood osmolarity
-Aldosterone causes both salt and water reabsorption and doesn’t change blood osmolarity
Epidermis
-the surface epithelium of the skin
-Subdivided into layers called strata
-From deepest layer outward: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum
Stratum Basale
-deepest layer (“the base”)
-contain stem cells and responsible for proliferation of keratinocytes, the predominant cells of the skin, that produce keratin
Stratum spinosum
-gives epidermis its strength and holds cells tightly together to prevent tearing of the skin
-site of Langerhans cells
-just above stratum basale
Stratum granulosum
-keratinocytes die and lose their nuclei
-just above stratum spinosum
-help to form waterproof barrier that functions to prevent fluid loss from the body
Stratum lucidum
-only present in thick, hairless skin, such as the skin on the sole of the foot or palm of the hands, and is nearly transparent
-just above stratum granulosum when present
Stratum corneum
-outermost layer of the epidermis (the surface)
-contains up to several dozen layers of flattened keratinocytes, forming a barrier that prevents invasion of pathogens and helps to prevent loss of fluids and salt
Cells of the epidermis
-keratinocytes, melanocytes, and Langerhans cells
Keratinocytes
-resistant to damage and provides protection against injury, water, and pathogens
-Calluses, fingernails, and hair are all formed from this
Melanocytes
-found in stratum basale
-Produce melanin, a pigment that serves to protect the skin from DNA damage caused by ultraviolet radiation
Langerhans cells
-special macrophages that reside within stratum spinosum
- Present antigens to T-cells in order to activate the immune system
Dermis
-middle layer of skin
-Papillary layer: consists of loose connective tissue
-Reticular layer: below papillary layer and more dense
-Sweat glands, blood vessels, and hair follicles originate in the dermis
-Most sensory receptors are also located in dermis
Merkel cells (dermis)
-sensory receptors present at the epidermal-dermal junction
-Responsible for deep pressure and texture sensation
Meissner’s corpuscles
respond to light touch
Ruffini endings
respond to stretch
Pacinian corpuscles
respond to deep pressure and vibration
Hypodermis
-deepest layer of skin
-Layer of connective tissue that connects the skin to the rest of the body
-Contains fat and fibrous tissue
Thermoregulation
-Achieved by sweating, piloerection, vasodilation, and vasoconstriction
-Vasodilation occurs at the same time as sweating to maximize heat loss. Brings a large quantity of blood to the skin, which accelerates evaporation of sweat
Sweating
-controlled by the autonomic nervous system
-Postganglionic sympathetic neurons that utilize acetylcholine innervate sweat glands and promote the secretion of water with certain ions onto the skin
-Heat is then absorbed from the body as the water molecules undergo a phase change to evaporate
-It is this evaporation of water that cools the skin
Thermoregulation in cold conditions
-Arrector pili muscles contract, causing hairs to stand on end which helps trap a layer of heated air near the skin
-The arterioles that feed the capillaries of the skin constrict, limiting the quantity of blood reaching the skin
-Skeletal muscle may contract rapidly causing shivering; Shivering requires a sizable amount of ATP
-Layer of fat just below the skin also helps keep the body warm
Skin and osmolarity
The skin is relatively impermeable to water which prevents not only the entrance of water through the skin but also the loss of water from the tissues
