Renal and Reproductive Physiology Review

Renal Anatomy and Physiological Structure

• Renal Fat Layers:

  • Perirenal Fat: This layer provides cushioning for the kidney and is responsible for anchoring the organ in its anatomical position.
  • Pararenal Fat: This type of fat is located external to the renal fascia.

• Protective and Functional Layers:

  • Renal Capsule: The outermost portion of the kidney; it serves as a protective barrier against infection.
  • Renal Cortex: The granular layer of the kidney, which contains a high density of blood vessels.
  • Renal Medulla: The layer containing most of the medullary pyramids, which are filled with nephrons.

• Kidney Dimensions and Location:

  • Size: The human kidney is approximately $12$ units tall (or long), $6$ units wide, and $3$ units thick.
  • Location: The kidneys are located in the retroperitoneal space (behind the peritoneum and the stomach area) and are protected by the $11^{th}$ and $12^{th}$ ribs. Their anatomical position is often described in relation to vertebrae $T11$ and $T12$.

Renal Physiology and Substance Transport

• Transport Mechanisms:

  • Passive Diffusion: A movement process that requires zero energy input.
  • Primary Active Transport: Requires direct energy in the form of ATP. A specific example is the sodium-potassium pump, which moves $3$ sodium ($Na^+$) ions out of the cell and $2$ potassium ($K^+$) ions into the cell for every $1$ molecule of ATP consumed.
  • Secondary Active Transport: Moves moieties (substances) by utilizing the movement of sodium.
    • Symport (Cotransport): Occurs when a moiety moves in the same direction as sodium. Substituted examples include glucose and water.
    • Antiport: Occurs when moieties move in opposition to sodium. Examples include potassium ($K^+$) and hydrogen ($H^+$) ions.

• Hormonal Influence on Transport:

  • Aldosterone: This hormone promotes the retention of sodium and water while simultaneously promoting the secretion (excretion) of potassium. Potassium moves in opposition to sodium specifically under its influence.
  • Parathyroid Hormone (PTH): Affects calcium reabsorption in the distal convoluted tubules and the ascending limb of the loop of Henle.

• Nitrogenous Waste Products:

  • Urea: A product resulting from the metabolic breakdown of amino acids.
  • Uric Acid: A product resulting from the metabolic breakdown of nucleotides.
  • Creatinine: A product resulting from muscle metabolism, specifically the creatine phosphate pathway.

• Hormonal Regulation of Fluid Balance:

  • Atrial Natriuretic Peptide/Hormone (ANP/ANH): Released from the heart in response to increased blood volume. Its functional role is to decrease blood volume.
  • Antidiuretic Hormone (ADH): Responsible for fluid retention; its secretion is suppressed by alcohol consumption.

The RAAS Pathway and Glomerular Filtration

• Glomerular Filterability: The two primary factors determining which molecules can pass through the glomerular filter are molecular weight and the electrical charge of the molecule.

• Renin Secretion and Regulation:

  • Renin secretion is regulated via three mechanisms: internal autoregulation (tension of the afferent artery), the nervous system (sympathetic nerves), and the hormonal system (epinephrine, norepinephrine, and prostaglandins).
  • Renin (Angiotensinogenase): Produced by the kidney. It acts on Angiotensinogen, which is produced by the liver.

• The RAAS Process:

  1. The kidney releases renin (angiotensinogenase).
  2. Renin converts angiotensinogen into Angiotensin I.
  3. Angiotensin Converting Enzyme (ACE), which originates in the lungs, converts Angiotensin I into Angiotensin II.
  4. Angiotensin II acts as a potent vasoconstrictor (elevating blood pressure) and promotes the release of aldosterone.
  • This system is a survival mechanism typically activated during physiological crises such as dehydration or hemorrhage.

Clinical Renal Conditions and Urine Composition

• Urine Output Alterations:

  • Oliguria: Infrequent or low urine output. Causes include hypovolemia, hypotension (low blood pressure), obstructive nephropathy, and renal disease.
  • Polyuria: Excessive urine output. Causes include glycosuria, hyperglycemia, and hysterical intake of water (not necessarily diabetes).

• Urinary Pathologies and Abnormalities:

  • Incontinence: Involuntary loss of urine. Causes include laughing, coughing, sneezing, emotional stress, pregnancy, and neurodegenerative diseases.
  • Hydronephrosis: Swelling of the kidney caused by a backup of urine, often due to decreased fat causing the kidney to drop and kink the ureter.
  • Renal Hypoplasia: An underdeveloped kidney.
  • Nephrotic Syndrome: Characterized by protein in the urine, often caused by abnormal nephron development.
  • Oligomeganephronia: The presence of only a few nephrons which are significantly enlarged.
  • Cross Fused Ectopia: A condition where the kidneys are fused and situated on one side of the body's midline.
  • Horseshoe Kidney: Fusion of the kidneys at one pole (usually the lower pole), with the majority of each kidney on opposing sides of the midline.
  • Porphyria Variegata: A genetic disease characterized by purple-colored urine.

• Urine Constituents:

  • Normal: Should be $95\%$ water, plus electrolytes, salts, urea, uric acid, and creatinine.
  • Abnormal: Presence of blood, bacteria, white blood cells, glucose, or protein.
  • Color Changes: Normal urine is yellow. Abnormal colors can be caused by jaundice (yellow/orange), medications, beets, or asparagus.

Male Reproductive Anatomy and Physiology

• Sperm Production and Development:

  • Spermatogenesis: Completed during Meiosis II.
  • Sertoli Cells: These cells make the sperm.
  • Epididymis: The location where sperm mature and are stored.
  • Sperm Count: Average count is $1.2 \times 10^8$ (120 million) sperm per milliliter.

• Male Hormones and Cells:

  • Interstitial/Leydig Cells: Responsible for the production of testosterone.
  • Aldosterone: A steroid hormone made in the adrenal cortex.
  • Nitric Oxide: Helps sustain an erection.

• Sperm Movement and Semen Production:

  • Seminal Vesicle: Produces a sugary fluid to provide energy/nourishment for sperm.
  • Prostate Gland: Produces an alkaline fluid to neutralize pH.
  • Bulbourethral Gland: Produces a lubricant.
  • Semen Statistics: Average ejaculate volume is $3 \text{ to } 5\,ml$. Average pH of semen is $7.5$.

• Anatomy:

  • Vas Deferens: The structure severed during a vasectomy to prevent sperm from entering the semen.
  • Glans Penis: The intense tip of the penis.
  • Foreskin: The external skin that can be removed via circumcision.
  • Testis Capsule: Composed of two tissue layers: the Tunica vaginalis and Tunica albuginia.
  • Erectile Tissues: Corpora cavernosa and corpus spongiosum.
  • Spermatic Cord: Contains the venous plexus, nerves, testicular artery, and vas deferens.
  • Scrotal Muscles:
    • Dartos Muscle: Smooth muscle.
    • Cremaster Muscle: Skeletal muscle that draws the testes closer to the body for temperature regulation.

Female Reproductive Anatomy and Physiology

• Anatomy and Functions:

  • Cervix: The opening to the uterus that dilates during childbirth.
  • Uterus: The normal site of implantation and growth of the pregnancy.
  • Vagina: The female copulatory organ.
  • Clitoris: The female erectile organ.

• Hormones and Cycles:

  • Estradiol: Gets the body ready for parturition (childbirth), enlarges genitalia, and increases throughout pregnancy.
  • Progesterone: Produced by the Corpus Luteum; it causes the uterus to double or triple in thickness.
  • Human Chorionic Gonadotropin (HCG): Released by trophoblast cells about $8$ days post-fertilization. It is detectable in urine and prevents the corpus luteum from regressing.
  • Human Chorionic Somatomammotropin (HCS): Preserves glucose for the mother.
  • Follicular Phase: A surge in LH (Luteinizing Hormone) leads to increases in FSH (Follicle-Stimulating Hormone) and estradiol.
  • Unfertilized Egg: Becomes a polar body, which is defined as a discarded set of chromosomes.

• Physiological Effects of Pregnancy:

  • Weight gain, incontinence, nausea, amniotic fluid development.
  • Increased respiratory demands and shift in organ positions.
  • Distension of the abdomen.
  • Pituitary Gland: Increases in size by $50\%$.
  • Blood Volume: Increases by $50\%$.
  • Renal Changes: Increased GFR (Glomerular Filtration Rate) and increased urine output.

Sexually Transmitted Infections (STIs) and Contraception

• Viral vs. Bacterial STIs:

  • Bacterial: Can be treated and cured with antibiotics.
  • Viral: Treatment reduces symptoms and recurrence but does not necessarily cure the infection.
  • Viral Examples: HIV, HSV (Herpes Simplex Virus), HPV (Human Papillomavirus).
  • HSV Type 1: Commonly appears above the waist, specifically around the mouth (oral herpes).
  • HIV Treatment: HAART (Highly Active Antiretroviral Therapy).

• Contraceptive Methods:

  • Intrauterine Device (IUD): Small plastic pieces inserted into the uterus to prevent implantation.
  • Diaphragm: A rubber-like barrier that prevents fertilization.
  • Abstinence: The only method that is $100\%$ successful at preventing both pregnancy and STIs.

Questions & Discussion

• Question: Which where does PTH affect calcium reabsorption?

• Answer: Dual tubules—the distal convoluted tubules and then the ascending limb of the loop of Henle.

• Question: What is the perirenal fat?

• Answer: The cushioning for the kidney that also anchors it.

• Question: About how long, tall, and wide or thick is the human kidney?

• Answer: $12$ tall/long, $6$ wide, and $3$ thick.

• Question: What is the enzymatic name for renin?

• Answer: Angiotensinogenase.

• Question: What are some causes of oliguria?

• Answer: Hypovolemia, hypotension, obstructive nephropathy, and renal disease.

• Question: What are the three glands responsible for producing semen?

• Answer: The seminal vesicle (sugar), the prostate gland (alkaline), and the bulbourethral gland (lubricant).

• Question: In males, when does spermatogenesis get completed?

• Answer: In Meiosis II.

• Question: Which hormone is present in the urine about eight days after fertilization?

• Answer: HCG, released by trophoblast cells.