BIOL 22000 Lecture Notes - Lecture 10: Descending Limb Of Loop Of Henle, Extracellular Fluid, Oncotic Pressure
8 Jun 2018
School
Department
Course
Professor
1
Chapter 10 Homeostasis
10.1The Excretory System
• The excretory system serves many functions, including the regulation of blood pressure,
blood osmolarity, acid–base balance, and removal of nitrogenous wastes
• The kidneys play an essential role in these functions
ANATOMY OF THE EXCRETORY SYSTEM
• Each kidney contains a million nephrons
• All the nephrons empty into the renal pelvis, which narrows to form the ureter
• Urine travels through the ureter to the bladder
Kidney Structure
• The cortex is the kidney’s outermost layer, while the medulla
of the kidney sits within the cortex
• Renal hilum is a deep slit in the center of its medial surface
• Renal pelvis spans almost the entire width of the renal hilum
• The renal artery, renal vein, and ureter enter and exit
through the renal hilum
• Kidney has a portal system consists of two capillary beds in
series through which blood must travel before returning to the
heart
• The renal artery branches out, passes through the medulla,
and enters the cortex as afferent arterioles
• The highly convoluted capillary tufts derived from these
afferent arterioles are known as glomeruli
• After blood passes through a glomerulus, the efferent
arterioles lead blood away from afferent arterioles
• Capillaries surround the loop of Henle and are known as
vasa recta
• The kidney’s ability to excrete waste is intricately tied to
the specific placement on the structure around
Bowman’s capsule
find more resources at oneclass.com
find more resources at oneclass.com
2
Bladder Structure
• The bladder has a muscular lining known as the detrusor muscle
• For urine to leave the body, it must pass through two sphincters
o The internal urethral sphincter, consisting of smooth muscle, is contracted in its
normal state
▪ Because it is made of smooth muscle, it is under involuntary control
o The external urethral sphincter consists of skeletal muscle and is under
voluntary control
• Stretch receptors convey to the nervous system that the bladder requires emptying when
the bladder is full, causing parasympathetic neurons to fire, and the detrusor muscle
contracts
• This contraction also causes the internal sphincter to relax, and this reflex is known as the
micturition reflex
• Urination is facilitated by the contraction of the abdominal musculature, which increases
pressure within the abdominal cavity, resulting in compression of the bladder and
increased urine flow rate
OSMOREGULATION
• The kidney filters the blood to form urine
• The primary job of the kidneys is to regulate blood volume and osmolarity, by urinating
to increase osmolarity, or vice versa
• Kidney function may be divided into the three different processes: filtration, secretion,
and reabsorption
Filtration
• The nephron’s first function is filtration
• Fluid is filtered into Bowman’s space and the collected fluid is known as the filtrate
• The movement of fluid into Bowman’s space is governed by Starling forces, which
account for the pressure differentials in both hydrostatic and oncotic pressures between
the blood and Bowman’s space
• Under most circumstances, fluid will flow from the glomerulus into Bowman’s space
• Molecules or cells that are larger than glomerular pores will remain in the blood
o If blood cells or proteins are found in the urine, this indicates a health problem at
the level of the glomerulus
Secretion
• Nephrons can secrete salts, acids, bases, and urea directly into the tubule by either active
or passive transport
• The quantity and identity of the substances secreted are related to the needs of the body at
that time
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
10. 1the excretory system: the excretory system serves many functions, including the regulation of blood pressure, blood osmolarity, acid base balance, and removal of nitrogenous wastes, the kidneys play an essential role in these functions. Anatomy of the excretory system: each kidney contains a million nephrons, all the nephrons empty into the renal pelvis, which narrows to form the ureter, urine travels through the ureter to the bladder. Secretion: nephrons can secrete salts, acids, bases, and urea directly into the tubule by either active or passive transport, the quantity and identity of the substances secreted are related to the needs of the body at that time. Key concept: filtration: movement of solutes from blood to filtrate at bowman"s capsule, secretion: movement of solutes from blood to filtrate anywhere besides bowman"s capsule, reabsorption: movement of solutes from filtrate to blood. Nephron function: kidney wants to keep what the body needs and lose what it doesn"t, and concentrate the urine to conserve water.
