Anatomy and Physiology Study Guide for the HESI Exam

Reproductive System

The reproductive system is responsible for producing, storing, and delivering gametes (sex cells) for reproduction. It is also crucial in hormonal regulation and sexual development.

In males, the reproductive system produces sperm cells and delivers them to the female reproductive system for fertilization.
In females, the reproductive system produces eggs (ova), supports fertilization, and provides the environment for fetal development.

The fusion of a sperm cell and egg cell results in the formation of a zygote, which develops into an embryo and, eventually, a fetus.

Male

The male reproductive system is responsible for producing and delivering sperm, the male gamete. It consists of:

testes—paired organs housed in the scrotum that produce sperm and secrete the hormone testosterone
epididymis—a coiled tube on the back of each testicle where sperm mature before being transported (The final stage of sperm maturation occurs in the epididymis.)
vas deferens (sperm ducts)—a muscular tube that transports sperm from the epididymis toward the urethra
seminal vesicles—glands that produce fluid rich in fructose, which provides energy for sperm
prostate gland—produces an alkaline fluid that helps neutralize the acidity of the female reproductive tract, increasing sperm survival
bulbourethral (Cowper’s) glands—secrete a lubricating fluid that neutralizes acidic urine in the urethra before ejaculation
urethra—a tube that carries semen and urine out of the body through the penis

Sperm Production and Hormonal Regulation

The testes produce sperm in a process called spermatogenesis, which begins at puberty and continues throughout life.

Testosterone, the primary male sex hormone, stimulates:

sperm production
development of secondary sex characteristics, including increased body hair, muscle mass, deeper voice, and thicker skin and bones

During ejaculation, sperm mix with fluid from the seminal vesicles, prostate gland, and bulbourethral glands, forming semen. The semen is then expelled through the urethra in the penis.

Female

The female reproductive system produces eggs, facilitates fertilization, and supports pregnancy. It consists of:

ovaries—paired glands that produce eggs (ova) and female sex hormones
fallopian tubes—tubes that transport the egg from the ovary to the uterus (This is where fertilization by a sperm cell first occurs.)
uterus—a muscular organ where a fertilized egg implants and develops during pregnancy
cervix—a muscular ring at the lower end of the uterus, which dilates during labor to allow childbirth
vagina—a muscular canal that serves as the passageway for sperm, menstruation, and childbirth

Menstrual Cycle and Hormonal Regulation

The menstrual cycle is a 28-day process regulated by hormones to prepare the body for potential pregnancy. It includes:

follicular phase (days 1–13)
- The pituitary gland releases follicle-stimulating hormone (FSH), stimulating egg development in the ovary.
- Estrogen is released, thickening the uterine lining in preparation for a fertilized egg.
ovulation (day 14)
- A surge in luteinizing hormone (LH) triggers the release of a mature egg from the ovary into the fallopian tube.
luteal phase (days 15–28)
- The ovary produces progesterone, which maintains the uterine lining in case of pregnancy.
menstruation (if no fertilization occurs)
- The uterine lining sheds, resulting in menstrual bleeding.

If fertilization occurs in the fallopian tube, the fertilized egg (zygote) travels to the uterus, where it implants and develops into an embryo.

If fertilization does not occur, the uterine lining is shed, marking the beginning of the next menstrual cycle.

Urinary System

The urinary system, also known as the renal system, is responsible for removing waste, regulating fluid and electrolyte balance, and maintaining homeostasis in the body. It helps control blood pressure, pH levels, and red blood cell production through hormone secretion.

The urinary system consists of:

kidneys—filter blood to remove waste and regulate fluid balance
ureters—muscular tubes that transport urine from the kidneys to the bladder
bladder—stores urine until elimination
urethra—passage through which urine is expelled from the body

Kidneys: Filtration and Homeostasis

The kidneys are bean-shaped organs located on either side of the spine, just below the rib cage. Their primary function is to filter blood and produce urine through millions of microscopic filtering units called nephrons.

Each nephron consists of:

renal corpuscle—contains the glomerulus, a network of capillaries where blood filtration occurs
renal tubule—adjusts the concentration of filtered fluid by reabsorbing water and nutrients while secreting waste

The kidneys also play a crucial role in homeostasis through the following processes:

regulating blood volume and pressure by adjusting water retention and releasing renin, which influences blood vessel constriction
controlling electrolyte balance by adjusting levels of sodium, potassium, calcium, and other ions
maintaining acid-base balance by regulating pH through hydrogen ion and bicarbonate excretion
producing these hormones:
- erythropoietin (EPO)—stimulates red blood cell production
- calcitriol—the active form of vitamin D, which regulates calcium absorption
- renin—helps control blood pressure by triggering hormonal pathways

Urine Formation and Flow

Urine formation occurs in the kidneys in three main steps.

1. Filtration (Glomerular Filtration)

Blood enters the kidney through the renal arteries and reaches the glomerulus.
Water, electrolytes, glucose, and small molecules pass into Bowman’s capsule, forming filtrate.
Large molecules like proteins and blood cells remain in the bloodstream.

2. Reabsorption and Secretion (Tubular Processing)

As filtrate moves through the proximal tubule, essential substances (water, glucose, amino acids, and ions) are reabsorbed into the blood.
The loop of Henle concentrates urine by reabsorbing water and sodium.
The distal tubule fine-tunes electrolyte and pH balance, secreting hydrogen ions and other waste.

3. Excretion (Urine Flow Through the Urinary Tract)

Once urine is fully formed, it follows this path through the urinary system:

collecting ducts—used by nephrons to drain urine into the minor and major calyces
renal pelvis—a funnel-shaped cavity where urine collects before leaving the kidney
ureters—muscular tubes that transport urine from the kidney to the bladder via peristalsis
bladder—a muscular organ that temporarily stores urine until elimination
urethra—the final passage through which urine is expelled from the body

The Bladder: Storage and Elimination

The urinary bladder is a hollow, muscular organ that temporarily stores urine before elimination. It expands as it fills and contracts during urination, a process controlled by the detrusor muscle.

The bladder can hold 400 to 600 milliliters (about 13 to 20 ounces) of urine in the average adult before triggering the urge to urinate.
When full, stretch receptors in the bladder signal the brain to initiate urination.
Urine exits the bladder through the urethra, which is controlled by the internal and external urethral sphincters.