Comprehensive Notes on Excretory System, Kidney Function, Male and Female Anatomy, and Fetal Development

Excretory Functions of the Body

  • Metabolic pathways require ATP and produce byproducts like carbon dioxide (CO_2).
  • Lungs excrete CO_2.
  • Kidneys produce urine.
  • Blood tests can reveal levels of:
    • Creatine
    • Electrolytes
    • Uric acid (from DNA breakdown)

Uric Acid and Gout

  • Uric acid is a byproduct of nucleic acid breakdown; excess leads to gout.
  • Gout symptoms: toe, elbow, knee pain, often exacerbated by consuming fish and organ meats.

Water and Salt Balance

  • Kidneys maintain water and salt balance.
  • Key electrolytes: sodium (Na), potassium (K), and calcium (Ca).

Acid-Base Buffer System

  • Crucial for maintaining bodily pH balance.
  • The primary buffer system involves:
    • H_2O (water)
    • CO_2 (carbon dioxide)
    • HCO_3^- (bicarbonate)
  • If there's too much acid, the body can:
    • Break it down into water and gas.
    • Combine it with CO_3^{2-} to create a neutral charge.
  • Homeostasis: Maintaining a stable baseline is essential.
  • Normal pH inside the body: 7.4 (slightly alkaline).
  • Kidneys regulate pH; drinking alkaline water forces them to work in reverse to maintain balance.
  • It's better to drink regular water and not disrupt the kidney's natural regulation.

Hormones Secreted by Kidneys

  • Erythropoietin is a key hormone.
  • Released when oxygen levels or blood pressure is low.
  • Stimulates bone marrow to produce more red blood cells.
  • Kidneys play a vital role in blood pressure control.

Kidney Structure

  • Renal Hilum contains:
    • Renal artery
    • Renal vein
    • Ureter
  • Renal Cortex is the outer part of the kidney.
  • Renal Medulla is the inner part, subdivided into pyramids and columns.

Nephron: Functional Unit of the Kidney

  • Analogy: Osteon is to bone, as nephron is to kidney.
  • Components of the nephron include:
    • Bowman's capsule
    • Glomerulus
    • Proximal convoluted tubule
    • Loop of Henle (descending and ascending limbs, thick and thin parts)
    • Distal convoluted tubule
    • Collecting duct

Glomerular Filtration

  • Glomerulus (aka Roman cathode) is where initial urine formation takes place.
  • Afferent arteriole: Carries blood into the glomerulus.
  • Efferent arteriole: Carries blood out of the glomerulus and branches to form the peritubular capillary network.
  • Glomerular capillaries have fenestrations (small holes like a sieve).
  • Podocytes: Specialized cells covering the capillaries, controlling leakage through fenestrations.
  • Filtration slits: Spaces between podocytes where electrolytes and fluids leak into Bowman's space, which gets
    collected in the glomerular capsular space.

Function of Tubules

  • Proximal Convoluted Tubule is permeable to water.
  • Distal Convoluted Tubule is not permeable to water but actively transports sodium (requires ATP).
  • Aldosterone (from the adrenal glands) increases sodium reabsorption in the distal convoluted tubule.
  • Collecting Duct's permeability to water is regulated by antidiuretic hormone (ADH).
    • ADH increases water reabsorption; without it, water stays in the duct and is excreted.

Urine Formation Processes

  • Glomerular filtration: initial filtration of blood.
  • Tubular reabsorption: peritubular capillaries reabsorb substances the body needs (e.g., sodium).
  • Tubular secretion: peritubular capillaries secrete substances into the nephron (e.g., excess water).

Urinary Tract Infections (UTIs)

  • Common causes: insufficient water intake, holding urine too long.
  • Bacteria travel up the urethra to the bladder and, if untreated, to the kidneys (pyelonephritis).
  • Certain bacteria can alter the pH of urine, creating a favorable alkaline environment for their proliferation.

Filtration, Reabsorption, and Secretion Summary

  • Filtration: Salts, nutrients, nitrogenous wastes, and water are filtered.
  • Reabsorption: Water and glucose are reabsorbed.
  • Tubular secretion: Peritubular capillaries secrete substances back into the collecting system.
  • Diabetic patients may have glucose in their urine due to damaged peritubular capillaries failing to reabsorb glucose.

Concentration Gradient in the Kidney

  • Concentration gradient increases from cortex to deep medulla.
  • Controls movement of substances across membranes via diffusion and active transport.
  • Passive transport: High to low concentration.
  • Active transport: Requires ATP to move substances against the concentration gradient.

Hormonal Regulation of Blood Pressure

  • Juxtaglomerular apparatus: Located between the afferent arteriole and distal convoluted tubule; specialized cells for blood pressure control.
  • Renin-Angiotensin System:
    • Low blood pressure triggers renin secretion.
    • Renin converts angiotensinogen to angiotensin I.
    • ACE (angiotensin-converting enzyme) converts angiotensin I to angiotensin II.
    • Angiotensin II constricts arteries, raising blood pressure, and stimulates aldosterone production.
    • Aldosterone increases sodium reabsorption; water follows, increasing blood volume and pressure.
  • ACE inhibitors and angiotensin receptor blockers are drugs that lower blood pressure by interfering with this system.
  • Atrial Natriuretic Peptide (ANP):
    • Secreted by the heart's atria when blood pressure is high.
    • Inhibits renin secretion, leading to decreased sodium reabsorption and lower blood volume and pressure.

Factors Affecting Urine Water Content

  • Atrial natriuretic peptide, diuretics (e.g., Lasix, thiazides), and alcohol increase urine water content.
  • Alcohol inhibits antidiuretic hormone (ADH) secretion.
  • Caffeine inhibits sodium reabsorption.

Kidney Failure and Function

  • Many people live with one kidney.
  • Only half of one kidney needs to function for normal pH and electrolyte balance.

Male Reproductive Anatomy

  • Male reproductive organs are external.
  • Male urethra has three parts: spongy, membranous, and prostatic.
  • Prostatic urethra connects to the bladder.
  • Seminal vesicles and ductus deferens (ampulla) add fluid to the ejaculatory duct that connects to the prostatic urethra.
  • Sperm from the epididymis travel through the ductus deferens.
  • Vasectomy involves cutting the vas deferens.
  • Sperm production requires lower temperature, hence the external location in the scrotal sac.
  • Bulbourethral (Cowper's) gland releases lubricant.
  • Prostatic gland produces proteins and enzymes to sustain sperm.

Penis Structure

  • Corpora spongiosum surrounds the spongy urethra.
  • Corpora cavernosa are responsible for erection; damage can result in fracture.

Scrotal Muscles

  • Dartos muscle lines the scrotal sac and contracts when cold, raising the testicles.
  • Cremaster muscles along the spermatic cord also assist in raising the testicles.

Testicular Structure and Spermatogenesis

  • Seminiferous tubules inside the testicle are where sperm production takes place.
  • Sperm travel from the seminiferous tubules to the rete testes and then to the epididymis.
  • Spermatogenesis involves :
    • Mitotic division of spermatogonia (stem cells).
    • Meiotic division to produce haploid sperm by cutting yourself in half.
    • Sperm production starts at puberty and continues throughout life.
  • One primary spermatocyte yields four haploid sperm.

Sperm Structure

  • Sperm require many mitochondria for energy (ATP).
  • Acrosome is used to penetrate the ovum.

Female Reproductive Anatomy

  • Female reproductive organs are internal.
  • Vagina is posterior to the urethra and bladder.
  • Vesicouterine pouch is between the bladder and uterus.
  • Rectouterine pouch is between the uterus and rectum.
  • Urethra is shorter in females.
  • Cervix has external and internal os; Pap smears are taken from the cervix to check for cancer, there are squamous
    cells that can turn into cancer typically caused by smoking and sex (HPV).
  • Uterus has three layers: endometrium, myometrium, and perimetrium.
  • Uterine tube connects to the uterus and has infundibulum and fimbriae that surround the ovary; cilia help the
    egg to flow down through the tube.

Ovary and Follicle Development

  • Females are born with all the eggs they will ever have.
  • Follicle Development(Primordial, Primary, Secondary, and Graafian.) starts with Primordial follicles, then transforms to primary and secondary then lastly Graafian. Primary follicles are starting to develop walls of cells around the egg itself, with secondary follicles developing a chamber or space forming within the primary follicle. The final follicle, Graffian, is the follicle that is read to pop.
    *Oocytes, k, with a granulosa cell layer.
  • Ovulation: The corona radiata (cells around the oocyte) is released.
  • After ovulation: A corpus luteum that is left develops to form a corpus albicans as a result of scarring. These corpus albicans, or scarring is what ovaries look like to demonstrate that the ovary has ovulated several times, in the place where the egg left.
  • Unequal meiotic division: one haploid versus 4, and that results in polar bodies versus sperm cells (which is 4x). Then a Primary Oocyte become arrested in Prophase 1, until the meiosis stage is needed to finish the rest in meiosis one.
    A Secondary Oocyte then is suspended In Metaphase II.

Fertilization and Implantation

  • Life begins at fertilization when the sperm fertilizes the egg, creating a zygote. This zygote will implant on the wall, that by then has enough preparation for the growth and development of a new embryo.
  • Then after the sperm penetration, and Mitoti division bingo. Now you've got daughter cells. Yay. Now we're gonna make more of ourselves to turn into a baby. So, obviously, it's gonna be a lot tinier than that little dot that's on this picture. But essentially, by the time you're at four or five weeks, which is basically before a woman even realizes she's pregnant, there's enough differentiation that has happened for babies to have limbs, heart, the development of the nervous system, etcetera. By twelve weeks after the end of the first trimester pregnancy, you've got a baby you can hold in your palm of your hand. Okay?

Early Embryonic Development

  • After fertilization, the zygote divides to form a morula, then a blastocyst with an inner cell mass.
  • The blastocyst implants into the endometrium.

Gastrulation and Germ Layer Formation

  • The inner cell mass forms the yolk sac and amniotic cavity.
  • Three germ layers are developed: Ectoderm, mesoderm, and endoderm. The ectoderm later develops a neural place which becomes the cranium and spinal cord, creating divisions in the cavities.

Organogenesis

  • By the fifth week, major organ systems (GI system, lungs, heart) are present.

Placentation

  • The placenta develops to nourish the developing fetus.

Fetal Circulation

  • The fetal circulation:
    • From placenta dumps into the inferior vena cava, then right atrium. Some right atrial blood pumps via pulmonary to the Right Ventricle, and through a Foramen Ovale to the left.
    • Ductus arteriosus shunts blood from the pulmonary trunk to the aorta.
    • After the aorta, then it comes down to the Umbilical arteries, dumping the circulation back to the placenta.
  • Foramen ovale and ductus arteriosus shunt blood away from the lungs as gas exchange occurs at the placenta.
  • The foramen ovale eventually closes to become the fossa ovalis. The ductus arteriosus also shrivels and becomes the ligamentum arteriosum.