Anatomy and Physiology - Urine Formation and Reproductive Systems

Kidney Anatomy Review

Renal Capsule

• The kidney is enclosed by a capsule on its outer edge called the renal capsule.

Renal Cortex

• Deep to the renal capsule is the renal cortex, which forms the outer portion of the kidney.

Renal Medulla

• Deep to the renal cortex is the renal medulla.

• The renal medulla contains:

  • Renal pyramids

  • Renal columns (located in between the renal pyramids)

Nephron

• The most basic functional unit of the kidney is called the nephron.

Renal Corpuscle

• The nephron consists of the renal corpuscle.

Filtration

• Within the renal corpuscle, a process called filtration occurs.

• Filtration is the process where fluid is collected after passing a solution through a filter paper into a beaker. The collected fluid is called filtrate.

Filtrate

• The filtrate settles within the Bowman's space.

• The filtrate then travels through the loop of Henle until it exits the collecting duct.

Urine

• Once the filtrate exits the collecting duct, it is then called urine.

Urine Formation and Flow

• Filtrate from the distal convoluted tubule moves into the collecting duct.

• Fluid exiting the collecting duct is called urine.

• Urine flows from the collecting duct to the minor calyx, then to the major calyx, then to the renal pelvis, then to the ureter, then to the urinary bladder, and finally out of the body through the urethra.

Microscopic Processes in Nephron

• Three processes occur at the nephron level: filtration, tubular reabsorption, and tubular secretion.

• Filtration occurs in the renal corpuscle.

• Tubular reabsorption: Substances move from the renal tubular structures (loop of Henle, distal convoluted tubule, collecting duct) back into the peritubular capillaries to be retained in the body.

• Tubular secretion: Substances move from the peritubular capillaries into the renal tubular structures to be excreted in urine.

• Once urine enters the ureter, its composition is finalized.

Three Microscopic Processes

• Filtration

• Tubular reabsorption (pink arrows)

• Tubular secretion (orange arrows)

• Tubular reabsorption and secretion occur outside the renal corpuscle, between the renal tubular structure and the peritubular capillaries.

Examples

• Moving water, electrolytes, or amino acids from the proximal convoluted tubule to the peritubular capillaries is tubular reabsorption (FALSE if stated as tubular secretion).

• Moving water from the peritubular capillaries to the collecting duct is tubular secretion (TRUE).

• The direction of the arrow indicates whether it is tubular reabsorption or tubular secretion.

Nephron Types

• Two types of nephrons are based on the location of the renal corpuscle and the length of the loop of Henle.

• Cortical nephrons:

  • Renal corpuscle is located on the outer edge of the renal cortex.

  • Shorter loop of Henle.

• Juxtamedullary nephrons:

  • Renal corpuscle is located deeper in the renal cortex.

  • Longer loop of Henle.

Renal Corpuscle Structures

• The renal corpuscle consists of the Bowman's capsule and the glomerulus.

• Afferent arteriole vs. efferent arteriole in the glomerulus can be identified by size; models may not have labels.

• Juxtaglomerular (JG) cells are modified smooth muscle cells around the afferent arteriole.

• Macula densa cells are located in the distal convoluted tubule where it comes close to the Bowman's capsule.

Microscopic Processes and Nephron Structure

• Filtration, tubular reabsorption, and tubular secretion occur in various parts of the nephron.

• Renal corpuscle: inverse letter C.

  • The grid inside the Bowman's capsule is the glomerulus.

  • PCT: proximal convoluted tubule.

  • Loop of Henle: thick descending, thin descending, thin ascending, thick ascending.

  • DCT: distal convoluted tubule.

  • Collecting duct leads to urine.

  • Peritubular capillary surrounds the nephron.

• Moving substances from the PCT to the peritubular capillary is tubular reabsorption.

Tubular Reabsorption at PCT

• Water

• Solutes

• Amino acids

• 99% of glucose

• Overall reabsorption at the PCT is about 65%.

• PCT is the workhorse of the nephron.

Reabsorption Elsewhere

• Solute reabsorption in the ascending loop of Henle.

• Water reabsorption in the late distal convoluted tubule and collecting duct depends on ADH (Antidiuretic Hormone) and aldosterone.

• PCT and descending loop of Henle reabsorb water regardless of hormone presence.

• Counter current mechanism: opposing flow in the nephron.

Trigon

• The two ureters pierce on the left and right side of the urinary bladder and the urethra is starts at the bottom of the bladder. Connect the three dots makes a trigon.

Urethra Differences

• Females: only one part, the urethra.

• Males: urethra has three parts as it passes through different structures:

  • Prostatic urethra: passes through the prostate gland at the base of the urinary bladder.

  • Membranous urethra: pierces through a muscle that forms the pelvic floor.

  • Spongy (penile) urethra: pierces through the spongy tissue of the penis.

Male Reproductive System

• Epididymis: Sperm cells mature and learn how to swim.

• Vas deferens: Tube system that sperm cells move into from the epididymis.

• Seminal vesicle: Produces the majority of fluid found in ejaculate (seminal fluid).

• Semen is seminal fluid.

• Flow: Vas deferens -> Prostate gland -> Penile/spongy urethra.

Female Reproductive System

• Ovaries: Sex organs.

• Uterus: Womb.

• Uterine tube/Fallopian tube

• IgA is part of bodily secretions.

• Hormones associated with milk:

  • Prolactin: Milk production.

  • Oxytocin: Milk secretion.

Gonads and Gametes

• Males: Testes

• Females: Ovaries

• Male gonads (testes), female gonads (ovaries).

• Sex cells are called gametes.

  • Male sex cells: Sperm cells.

  • Female sex cells: Eggs or oocytes.

Somatic Cells

• Non-sex cells are referred to as somatic cells.

• Examples: Liver cells, skin cells.

Cell Division

• Gametes use meiosis (cell division for sex cells).

• Somatic cells use mitosis.

• Gametogenesis is the general term for sex cell production.

  • Spermatogenesis: Specific to male sex cell (sperm) production.

  • Oogenesis: Specific to female sex cell (egg) production.

Female Reproductive Cycle

• Reproductive age cycles occur monthly from day 1 to day 28.

• Day 14 is the mid-cycle.

• A surge of luteinizing hormone (LH surge) signals the release of a mature oocyte (ovulation).

• Menopause: When a female stops producing and releasing eggs each month.

• Misses in the reproductive years: Pregnancy (unless proven otherwise).