Kidney Microanatomy and Embryology (W1 1/11) Flashcards
Blood supply to the kidney?
- Start as renal arteries
- Branch into inter-lobar areteries
- Then Arcuate arteries are the vessels on top of the pyramids
- Then branch into inter-lobular arteries
- Inter-lobular arteries have afferent arterioles coming out of them
- Afferent arterioles lead to the glomerulus. (A first in alphabet, A first in coming before glomerulus).
- Efferent arterioles come after the glomerulus. (E after A in alphabet).
- See ‘renal micro-circulation’ slide for histological image or add image later.
- See histological image of glomerulus and add and label
LO: Describe the clinically relevant embryology of the kidneys and urinary tract
Please see the liked/ thumbs up youtube video on kid.em on my likes playlist
Day 0/1: Fertilised single celled embryo = zygote
Day 2/3: Cleavage/ Cell division. Becomes 16 cells/ morula
Day 4: A blastula, in general, is a spherical mass of cells surrounding a fluid formed after 5–8 days of fertilization. In mammals, the blastula is specifically called a blastocyst. First differentation: Inner cell mass (embryoblast) and outer cell mass (trophoblast).
Day 5-11: Implantation on uterine wall
Day 11: Bilaminar disc: refers to the epiblast and hypoblast evolved from the embryoblast. The epiblast are like jam (epiblast) and peanut butter (hypoblast) with two pieces of bread sandwiching them (the yolk sac and amnion).
Day 12-14:
- Placenta formation begins
- Elongation of embryo begins
- Primitive streak formation (embryo literally deveops a streak)
Day 15: Gastrulation (see image)
- Epiblast cells migrate towards primitive streak
- Cells enter primitive streak and differentiate into endoderm or mesoderm
- Cells that do not migrate through primate streak differentiate into ectoderm
- Right so we have mesoderm in middle of the embryo, ectoderm on top, and endoderm at the bottom. (ecto-meso-endo)
- As ectoderm matures it pinches and forms the neaural tube. The mesoderm matures to the paraxial mesoderm (which gives rise to skeletel muscle, tendons and cartilage) , the intermediate mesoderm (which gives rise to the kidneys, gonads/ ovaries or testicules and genitals) , and lateral plates (which develop into circulatory vessels).
- The intermediate mesoderm has 2 transitory stages. The first t.s is the pronephros. The kidney develops from top to bottom.
- By 4 weeks, the pronephros is degraded and the next stage takes over- mesonephros. The mesonephros is made of a duct system called the mesonephric duct and mesonephric tubules. The mesonephros is surrounded by tissue called the nephrogenic cord. The mesonephros will eventually become the genitals.
- From the nephrogenic cord the uretal bud forms. This is the metanephros stage. The adult kidney. The uretal bud forms the collecting ducts (including the minor and major calyces, ureter and renel pelvis) by bifurcating.
- The sacra/ bottom part of the nehrogenic cord will become metanephric blastula, and circle the uretal bud and form vesicles. This is the adult kidney, functional by week 12.
Then migration of the kidneys happens. At week 6 the kidneys are near the bladder, with their hilum and ureters facin the front. The kidneys move up to where the adrenal glands are using transient arteries. By week 9 the hilum and the ureters are facing medially. (see image)
Kidney Defects (can be developmental or migrational)
Developmental:
Renal agenesis: Kidneys fail to develop (missing) – can be unilateral or bilateral
Unilateral Renal Hypoplasia: not developed properly
Super-numerary Kidney: more than 2
Migrational:
Renal ectopia (ectopic kidney): failure in migration – kidney can remain in pelvis instead of migrating to posterior abdominal wall
Abnormal rotation: hilum faces ventrally rather than medially. As it did in early development.
Crossed Ectopia: switched ureters with each other.
Supernumary (multiple) renal vessels: Failure of regression of transient renal vessels – ureter can be trapped by vessels – leads to hydronephrosis – build up of urine
LO: Describe the microanatomical features of the kidney and urinary tract
(Names you need to know)
- The renal pelvis is the part of the ureter in the kidney. Major function: to act as a funnel for urine flowing to the ureter.
- Calyces: Parts of the kidney that collect urine before it passes further into the urinary tract. The calyces are part of the renal pelvis, that connect the innermost part of the kidney to the ureters and, from there, to the bladder.
- Ureter: the duct by which urine passes from the kidney to the bladder
- Renal vein carries blood away from the kidney
- Medullary pyramid: Cone-shaped tissues of the kidney. In humans, the renal medulla is made up of 10 to 18 of these conical subdivisions.
- Renal cortex: the outer layer of the kidney.
- The aorta supplies the kidney with oxy. blood. The aorta divides/ birfurcates into two branches, the left and right renal arteries, supplying each kidney. In the kidneys, the renal artery divides into 5 segmental arteries. The segmental arteries divide into inter-lobars. They are situated either side of every medullary pyramid. Then they divide into arcuate arteries (horizontal on top of the medullary pyramids). This then becomes afferent arterioles connected to the glomerulus.
- Renal Column: A medullary extension of the renal cortex in between the renal pyramids. It allows the cortex to be better anchored.
- Renal Papilla: the point of each medullary pyramid.
- Renal Capsule: refers to a thin membranous protective covering over the external surface of the left as well as the right kidney. Within the hilum of the kidney this capsule becomes continuous with the connective tissue linings of the calyces and the renal pelvis.
LO: Describe the functional properties of urothelium
Urothelium structure changes depending on volume of urine
Impenetrable to urine, even when stretched
Is in non-distended state when tract is empty
In distended state when full of urine (cells are flattened in distended state)
Urothelium is stratified (layered) epithelium: ]
- the cell at the top are umbrella cells (dome shaped and have multiple nuclei)
- In the middle have intermediate cells (which are square shaped)
- At the bottom have basal cells (cuboidal)
Nephrons
- Afferent arteriole
- Glomerulus: The diameter of the afferent (incoming) arteriole is greater than the diameter of the efferent arteriole. The pressure of the blood inside the glomerulus is increased due to the difference in diameter of the incoming and out-going arterioles. This increased blood pressure helps to force the following components of the blood out of the glomerular capillaries: water, salt, glucose, urea. This means glomelur filtrate contains all the materials present in the blood except blood cells and most proteins - which are too large to cross the basement membrane of the glomerulus. Only about 1% of the glomerular fitrate actually leaves the body because the rest (the other 99%) is reabsorbed into the blood while it passes through the renal tubules and ducts. The glomerulus is surrounded by urinary space and then Bowman’s Capsule.
- Bowman’s Capsule:
- Efferent arteriole (Blood goes to inferior vena cava)
- Proximal Convulated Tubule: (where the filtrate goes)
- Ascending limb of loop of Henle:
- Descending limb of loop of Henle:
- Distal Convulated Tubule:
- Pertibular capillaries/ Vasa Recta
- Arcuate vein - Inter-lobar vein - Renal vein - Inferior vena cava
Glomerulus
The capillaries of the glomerulus are surrounded by mesangium. Theses are cells surrounding the glomelular capillaries. The capillaries are made of fenestrated epithelium (has holes).
****** Do later after watching the nephrology playlist: include proximal convulated tubule
Cortical Labyrinth
The cortex of the kidney can be further divided. Medullary rays are lines of the medulla that spike into the cortex area. The cortical labryinth is the normal area. In the cortical labrinth the PCT has thick walls (coarse control of reabsorption - 67% of all H2O, HCO3, Na, Cl, 100% of glucose).
Juxta-glomerular Apparatus
Cells that sit between the glomerulus and distal convulated tubule. It detects filtrate rate and quality.
What is the lower urinary tract?
Everything apart from the kidneys. So the Ureters (including the part of the ureter in the kidneys- the renel pelvis) Bladder, Aorta and branching arteries, and the Urethra. All have the same general structure.
- Outer layer is tight, circular, spiral muscle
- Then have loose, longitudinal, spiral muscle
- Sub-mucosa
- Inner-most layer is urothelium
In the ureters: urine forced down to bladder by peristalsis. Peristalsis requires contraction of smooth muscle - ureter walls are highly muscular
In the bladder: It has urothelium, but the sub-mucosal layer is made of fibro-collagen, and the smooth muscle layer has three layers.
LO’s
- Describe the microanatomical features of the kidney and urinary tract
- Describe the functional properties of urothelium
- Describe the clinically relevant embryology of the kidneys and urinary tract
