RENAL SYSTEM

renal system 1 - lecture 15

OVERVIEW OF KIDNEY FUNCTION

  • in general animals have a tube-like structure ( composed of multiple cell types)

    • that’s involved in ion balance and fluid balance

  • vertebrates have multiple roles in homeostasis :

    • ion balance

    • osmotic balance

    • blood balance

    • pH of the blood

    • excretion of unwanted products

    • hormone production

  • strong link between the cardiovascular system + renal system

EVOLUTION OF RENAL SYSTEM

  • ancient aquatic animals use cellular transport, maintaining differences between ICF and sea water ( e.g. by ion pumps)

  • development of an OUTER EPITHELIAL LAYER was a major evolutionary step (ecf separated from the external environment)

  • through evolution increasingly complex mechanisms emerged for generating differences between the ecf and the sea water (external environment)

  • three renal structures are observed during vertebrate evolution and development 😀

    DEVELOPMENT

    ( structures get progressively more complicated during development)

    1. pronephros

      • (simplest kidney)

      • blunt endings to tubes + cilia presence

    2. mesonephros

      • first bowman’s capsules appear

      • ( c shaped cup) which increases SA

    3. metanephros (kidney)

      • emergence of ureter

      • many smaller nephrons clustered in kidney

EVOLUTION

  • through evolution there is an increase in numerous nephrons ( more efficient filtration units)

glomerulus = network of capillaries

  • endothermy is the ability of an organism to regulate its body temperature internally, maintaining a constant temperature regardless of external conditions.

  • with the shift to endothermy, the mass of kidney remains consistent even when we take into account the body size

  • the size essentially makes sense in all organisms.

  • an increase is seen in the filtration + reabsorption rates

    • nephrons are more densely packed in more complex organisms

    • birds and mammals show the greatest efficiency in filtration and reabsorption rates

      renal cells initially evolved to transport nutrients but developed additional functions

EVOLUTION OF THE NEPRHON

  • the basic structure of the nephron is largely conserved between species

    • birds contain both reptilian and mammalian type of neurons

    • all mammals have a loop of Henle, but the length of the loop of Henle varies through species ( longer in species that are in harsh conditions)

    • the basic nephron structure in vertebrates =

      • filtering unit (glomerulus capsule)

      • proximal + distal tube

salt transport in different classes

mammals - no additional salt transport organs

INTRODUCTION TO THE RENAL SYSTEM

  • kidneys are critical for maintaining mammalian extracellular fluid composition

  • the nephron is the key functional unit

  • nephrons have a complicated structure

  • regions are specialized for different functions

INTRODUCTION TO THE NEPRHON

  • lots of parts here

  • the filtration rate is determined by the afferent arteriole + efferent arteriole because of the pressure gradient they have

  • the space between the glomerulus and glomerulus capsule = mass filtration ( everything except cells, blood cells + proteins will get into your kidney)

    • not a fine process, think of it as a massive recycling point

  • the loop of Henle region all about creating gradients that help to conc urine

  • tweaking of filtration to get osmolarity happens at the end section

    urine formation

  • flow regulation - the diameter of the tube, arterioles ( packed with smooth muscle ), ideally suitable - pressure gradients

  • regulated water absorption - presence of aquaporins

  • mass filtration - more villi, more membrane, more blood vessels all clustered up tightly knotted = surface area

  • mass reabsorption - thin membrane, surface, convoluted (windy) tubule = gives surface area, mitochondria as energy is needed to move substances around, leaky gap junctions

renal system 2 - lecture 16

structure and function in the nephron

filtration at the glomerulus

  • lots of blood vessels connected to BC

  • filters proteins ( because they are negative + too big ) + cells

  • glomerular capillaries are very leaky

  • covered in podocytes

    • specialized epithelial cells

    • have “feet” connected by slit junctions - part of filtration barrier

gfr - glomerular filtration rate

  • determined by:

    1. permeability of the filtration barrier (only changes in disease)

    2. surface area for filtration ( only change during development)

    3. glomerular filtration pressure (changes day to day, variable in the short term)

      • first two aspects don’t change too much.

forces contributing to filtration pressure

  • filtration = the movement of fluid from glomerulus → bowman’s capsule

  • filtration across the glomerulus is determined

    • hydrostatic pressure (pressure exerted by fluid) - promotes fluid moving into the capsule

    • oncotic pressure ( pressure exerted by water moving down its concentration gradient)

    • there is always a net filtration ( fluid movement into nephron) in a healthy kidney

Water pressure is lower in Bowman's capsule than in the capillary due to the following reasons:

  1. Filtration Process: In the glomerulus, blood pressure forces water and solutes out of the capillaries into Bowman's capsule, creating a filtration pressure.

  2. Resistance: The efferent arteriole creates resistance, maintaining higher pressure in the capillaries.

  3. Volume and Space: Bowman's capsule has a larger volume and space, leading to a decrease in pressure compared to the confined space of the capillaries.

This difference is crucial for effective filtration in the kidneys.

bulk reabsorption of the proximal tubule

most reabsorption in the nephron happens here

several factors increase permeability and or transport

  • dense capillary network nearby

  • winding structure

  • extensive microvilli

  • high numbers of mitochondira

  • leaky “tight” junctions

  • many + diverse transporters

ions in ECF AND ICF

Differences between Symport and Antiport:

  • Symport:

    • Transports two different substances in the same direction across a membrane.

    • Example: Glucose and sodium ions in intestinal cells.

  • Antiport:

    • Transports two different substances in opposite directions across a membrane.

    • Example: Sodium-potassium pump (Na+/K+ pump).

Key Points:

  • Both are types of cotransport mechanisms.

  • Symport moves substances together, while antiport exchanges them.

introduction to the loop of Henle

  • enables production of small volume of conc urine

  • recovers solutes from filtrate

    • descending - permeable to water but not salt

    • ascending - impermeable to water + active transport of salt ← needs a lot of energy

      • whether it stays dilute or more conc depends on the collecting duct

water reabsorption in the descending loop of henle

water moves down its electrochem grad through aquaphorins

water conc depends on conc of all dissolved solutes

water follows the solutes

  • if there is a higher solute conc outside the tubule there is a higher water conc inside the tubule

  • water will flow out of tubule

  • filtrate becomes more conc deeper in the loop of Henle

active solute reabsorption in the ascending loop of henle

  • alot of salt taken out to provide a dilute conc

  • thick ascending limb expresses mnay transporters Na+ CL from tubule back into the blood

  • depends on K+ recylcling because - transporter will only will if all ions are present

summary of urine production