Jackson 5 Flashcards
. Other renal functions include:
Gluconeogenesis
Production of hormones
Kidney produces
erythropoietin – acts in the bone marrow to stimulate synthesis of new erythrocytes
renin – part of renin-angiotensin-aldosterone cascade to regulate blood pressure
1,25-dihydroxyvitamin D – regulate calcium absorption
renin –
part of renin-angiotensin-aldosterone cascade to regulate blood pressure
1,25-dihydroxyvitamin D –
regulate calcium absorption
The actual proportion of the total body water that the kidney “sees” and process is
very small. However, changes in the one, small compartment affected by kidney function can ultimately affect the other compartments.
ESRD patients have a reduced ability to
eliminate nitrogenous wastes (urea) and excess nitrogen is converted to ammonium.
ESRD patients;
The excess ammonium has
direct effects on health – the blood is alkalized which leads to an increased pH in the oral cavity.
Manifestations of renal disease on oral health include:
ammonia breath –
gingival enlargement –
xerostomia –
tooth problems
-premature loss
- narrowing pulp chambers
- necrosis beneath fillings or crowns
Contraindications for ESRD patients:
nephrotoxic drugs such as tetracycline, acyclovir, aspirin, NSAIDs
increased susceptibility to bleeding due to destruction of platelets
in the renal medulla – there are
portions of nephron tubule involved with concentration and collection of urine
Each kidney contains
~1.2 x 106 nephrons.
A nephron includes a cluster of
capillaries and a long, hollow tube with a wall that is one cell layer thick.
Parts of a nephron
renal corpuscle = glomerulus + capsule
proximal (convoluted) tubule
loop of Henle
distal (convoluted) tubule
collecting duct – shared by several nephrons
The position of a nephron with respect to the
cortical and medullary regions of the kidney can vary somewhat. There are two types of nephrons that differ in the position of the renal corpuscle and the length of the medullary tubules
superficial or cortical nephrons -
juxtamedullary nephrons -
Regulating blood composition involves three renal processes
Filtration
Secretion
Reabsorption
- filtration – solutes (and the water they are dissolved in) pass from the
blood into the tubular fluid in the renal capsule (Bowman’s space)
filtration occurs in the
glomerular capillaries; 15-20% of plasma entering glomerulus is filtered
blood leaving the glomerular capillaries then flows into
peritubular capillaries (vasa recta)
- secretion – substances are transported from the blood in the
peritubular capillaries into the tubular fluid
- reabsorption – substances are transported from the tubular fluid into the blood in the
peritubular capillaries
Re: renal corpuscle =
glomerulus + renal capsule
A glomerulus is a dense capillary bed where filtration occurs
surrounded by
renal capsule (or Bowman’s capsule) which collects the filtrate from the blood entering via the afferent arterioles
filtered blood leaves via
efferent arterioles and flows into peritubular capillaries
Blood flow through the glomerulus is regulated by several mechanisms
smooth muscle contraction in afferent or efferent arterioles
response of the juxtaglomerular apparatus (JGA) located at the intersection of the macula densa of distal tubule with afferent and efferent arterioles –
sympathetic nervous system –
juxtaglomerular apparatus (JGA) secretes the hormone
renin which regulates systemic blood pressure, and, therefore, glomerular blood flow
Proximal convoluted tubule
The proximal tubule drains the renal capsule
reabsorbs
2/3 of flitered salt and water
reabsorbs all filtered glucose and amino acids
some diurectics will act here
Loop of Henle
Loop of Henle can be divided into three limbs or segments
thin descending limb
thin ascending limb
thick ascending limb (TAL)
The loop is the site of
countercurrent multiplication needed to produce concentrated urine, but the loop itself produces a dilute filtrate.
Very powerful diuretics work in the
Loop of Henle.
Distal convoluted tubule
The distal tubule drains the
loop of Henle
continued reabsorption of solutes –
regulation of calcium –
site of action for some diuretics
Collecting duct
Collecting duct – collects fluid from
multiple nephrons
Collecting duct
extends from
cortex through the medulla
Collecting duct
regulates
sodium, potassium, and water
some diuretics act here
Renal clearance is the
rate of excretion of a solute through the kidney, expressed as amount per unit time.
=
renal clearance represents the
volume of plasma from which all of a particular substance is removed to the urine (i.e. cleared), e.g. 100 ml/min
clinically important concept for monitoring renal function
Glomerular filtration rate is the amount of blood filtered by the
kidney, expessed as volume per unit time.
Renal clearance can be used to measure glomerular filtration rate (GFR) based on three criteria
- the substance must be freely filtered in the glomerulus
- the substance is not secreted
- the substance is not reabsorbed
in a normal kidney, GFR (from all nephrons) is
125 ml/min or 180 L/day in females; 90-140 ml/min in males
Inulin and creatinine are substances that can be used to measure
renal clearance
inulin –
small polysaccharide; freely filtered and not secreted or absorbed
creatinine –
product of muscle metabolism; freely filtered, not reasbsorbed, almost no secretion; normal creatinine levels < 1+ 0.5 mg/dl; if > 10 → requires dialysis
Glomerular capillaries are
fenestrated;
podocytes (cells) around the
capillaries form filtration slits
filtrate is
acellular and essentially protein-free
————————- are freely filtered
glucose, salts, and amino acids
size is a factor:
< 20 Ǻ freely filtered, > 42 Ǻ not filtered
charge is also a factor
basal lamina (basement membrane) is negatively charged so filtration of moderately-sized, negatively-charged solutes is limited
Filtration occurs due to
pressure differences between the blood in the capillaries and the fluid in the capsule (Starling forces).
Pressure comes from two sources:
hydrostatic pressure = pressure due to fluid
P in capillaries > P in capsule fluid
oncotic pressure (π) – pressure due to solutes in fluid (including those not dissolved) π in capillaries > π in capsule fluid
Net filtration pressure favors filtration from
blood into the capsule fluid
GFR ∞ (PGC – PBS) – (πGC – πBS) note that πBS = 0
GFR is affected by
blood flow into and out of the glomerulus, and P gradient is critical to maintain filtration
Despite changes in systemic blood pressure, renal blood flow (RBF) remains
fairly constant
because RBF remains constant, GFR remains constant
Autoregulation involves intrinsic mechanisms that adjust bloodflow through the glomerulus; it is achieved by two primary mechanisms:
- myogenic mechanism – vascular smooth muscle tends to contract when it is stretched, and relax when not stretched
constriction or dilation of smooth muscle in afferent or efferent arterioles has contrasting effects on RBF
- tubuloglomerular feedback – feedback from the JGA adjusts afferent arteriole diameter and, thus, GFR
↑ GFR à ↑ NaCl in tubular fluid à ↑ NaCl at macula
densa à ↑ resistance in afferent arterioles à ↓ GFR
myogenic mechanism –
vascular smooth muscle tends to contract when it is stretched, and relax when not stretched
- tubuloglomerular feedback –
feedback from the JGA adjusts afferent arteriole diameter and, thus, GFR
Also have extrinsic factors regulating RBF and GFR; some will be discussed in further detail in subsequent lectures
diet –
dehydration or hemorrhage –
sympathetic nervous system –
angiotensin II, aldosterone, and natriuretic peptide -
