Anatomy Course

May 23 2025

Male Reproductive System: Structure & Function

What is the male reproductive system?

The male reproductive system consists of a group of organs that make up the reproductive system and urinary system.
The male reproductive system contains internal and external parts. Internal parts are inside your body, and external parts are outside your body.
Together, these organs help you pee, have sexual intercourse and make biological children.

1. External – male reproductive parts

Most of the male reproductive system is on the outside of your abdominal cavity or pelvis. The external body parts include your penis, scrotum and testicles. Other names for these parts are genitals or genitalia.

~ Penis:

The penis is the male organ for sexual intercourse.

It contains many sensitive nerve endings, and it has three parts:

1. Root-

The root is the base of your penis.
It attaches to the wall of your abdomen.

2. Body (shaft)-

The body has a shape like a tube or cylinder.
It consists of three internal chambers: the two larger chambers are the corpora cavernosa, and the third chamber is the corpus spongiosum.
The corpora cavernosa run side by side, while the corpus spongiosum surrounds your urethra.
There’s a special, sponge-like erectile tissue inside these chambers. The erectile tissue contains thousands of spaces. During sexual arousal, the spaces fill with blood, and our penis becomes hard and rigid (erection). An erection allows you to have penetrative sex. The skin of our penis is loose and stretchy, which lets it change size when you have an erection.

3. Glans (head)-

The glans is the cone-shaped tip of our penis.
A loose layer of skin (foreskin) covers your glans.
Healthcare providers sometimes surgically remove the foreskin (circumcision).
In most people, the opening of the urethra is at the tip of the glans.
The urethra transports pee and semen out of your body. Semen contains sperm.
You expel (ejaculate) semen through the end of your penis when you reach sexual climax (orgasm).

When our penis is erect, our corpora cavernosa press against the part of our urethra where pee flows. This blocks our pee flow so that only semen ejaculates when we orgasm.

Normal size of the penis- Studies suggest that the average penis is about 3.5 inches (8.9 cm) when flaccid (soft) and a little more than 5 inches (13 cm) when erect.

~ Scrotum:

Our scrotum is the loose, pouch-like sac of skin that hangs behind your penis.
It holds your testicles (testes) as well as nerves and blood vessels.
Our scrotum protects your testicles and provides a sort of “climate-control system.”
For normal sperm development, your testes must be at a temperature that’s slightly cooler than body temperature (between 97 and 99 degrees Fahrenheit or 36 and 37 degrees Celsius).
Special muscles in the wall of your scrotum let it contract (tighten) and relax.
Our scrotum contracts to move your testicles closer to your body for warmth and protection.
It relaxes away from your body to cool them.

~ Testicles:

Our testicles (testes) are oval-shaped organs that lie in your scrotum.
They’re about the size of two large olives.
The spermatic cord holds your testicles in place and supplies them with blood. Most people have two testicles, on the left and right side of their scrotum.
Our testicles make testosterone and produce sperm. Within your testicles are coiled masses of tubes.
These are the seminiferous tubules.
The seminiferous tubules produce sperm cells through spermatogenesis.

~ Epididymis:

Our epididymis is a long, coiled tube that rests on the back of each testicle.
It carries and stores the sperm cells that your testicles create.
Our epididymis also brings the sperm to maturity — the sperm that emerge from your testicles are immature and incapable of fertilization.
During sexual arousal, muscle contractions force the sperm into your vas deferens.

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2. Internal – Male Reproductive Parts:

There are several internal (accessory) organs in the male reproductive system. They include:

~ Vas deferens:

Our vas deferens is a long, muscular tube that travels from the epididymis into our pelvic cavity,
just behind your urinary bladder.
Our vas deferens transports mature sperm to the urethra in preparation for ejaculation.

~ Ejaculatory ducts:

Each testicle has a vas deferens that joins with seminal vesicle ducts to form ejaculatory ducts.
The ejaculatory ducts move through your prostate, where they collect fluid to add to semen.
They empty into your urethra.

~ Urethra:

The urethra is the tube that carries pee from your bladder outside of your body.
If you have a penis, it also ejaculates semen when you reach orgasm.

~ Seminal vesicles:

Our seminal vesicles are sac-like pouches that attach to our vas deferens near the base of our bladder.
Seminal vesicles make up to 80% of your ejaculatory fluid, including fructose.
Fructose is an energy source for sperm and helps them move (motility).

~ Prostate gland:

Our prostate is a walnut-sized gland that rests below your bladder, in front of your rectum.
Our prostate adds additional fluid to ejaculate, which helps nourish sperm. Your urethra runs through the center of your prostate gland.

~ Bulbourethral (Cowper) glands:

Our bulbourethral glands are pea-sized structures on the sides of our urethra,
just below our prostate.
They create a clear, slippery fluid that empties directly into our urethra.
This fluid lubricates our urethra and neutralizes any acids that may remain from your pee.

Function

~ What does the urethra do?

The organs that make up the male reproductive system perform the following:

Produce, maintain and transport sperm cells and semen.
Sperm cells are male reproductive cells. Semen is the protective fluid around sperm.
Discharge sperm.
Produce and secrete male sex hormones.

~ How does the male reproductive system function?

The entire male reproductive system depends on hormones. Hormones are chemicals that stimulate or regulate activity in our cells or organs. The primary hormones that help the male reproductive system function include:

Follicle-stimulating hormone (FSH):

Our pituitary gland makes FSH.
FSH is necessary to produce sperm (spermatogenesis).

Luteinizing hormone (LH).

Our pituitary gland also makes LH.
LH is necessary to continue the process of spermatogenesis.

Testosterone:

Testosterone is the main male sex hormone.
It helps we develop certain characteristics, including muscle mass and strength, fat distribution, bone mass and sex drive (libido).

Disorders & Diseases:

Common conditions that affect the male reproductive system include:

Testicular cancer
Penile cancer
Prostate cancer
Sexually transmitted
infections (STIs)
Premature ejaculation
Male infertility
Erectile dysfunction
Priapism

Reference:

May 22 2025

Female Reproductive System: Structure & Function

saeedurrahmangroup Anatomy Course 1

What is the female reproductive system?

The female reproductive system is the female body parts that help us:

Have sexual intercourse
Reproduce
Menstruate

What are the parts of the female reproductive system?

The female reproductive anatomy includes both external and internal parts.

Internal – Reproductive Body Parts
External – Reproductive Body Parts

1. Internal – Reproductive Body Parts

~ Vagina:

Our vagina is a muscular canal that joins the cervix (the lower part of uterus) to the outside of the body.
It can widen to accommodate a baby during delivery and then shrink back to hold something narrow like a tampon.
It’s lined with mucous membranes that help keep it moist.

~ Cervix:

Our cervix is the lowest part of your uterus.
A hole in the middle allows sperm to enter and menstrual blood to exit.
Our cervix opens (dilates) to allow a baby to come out during a vaginal childbirth.
Our cervix is what prevents things like tampons from getting lost inside your body.

~ Uterus:

Our uterus is a hollow, pear-shaped organ that holds a fetus during pregnancy.
Our uterus is divided into two parts: the cervix and the corpus.
Our corpus is the larger part of your uterus that expands during pregnancy.

~ Fallopian tubes:

These are narrow tubes that are attached to the upper part of your uterus and serve as pathways for our egg (ovum) to travel from your ovaries to your uterus.
Fertilization of an egg by sperm normally occurs in the fallopian tubes.
The fertilized egg then moves to the uterus, where it implants into your uterine lining.

~ Ovaries:

Ovaries are small, oval-shaped glands that are located on either side of your uterus.
Our ovaries produce eggs and hormones.

Female Reproductive System: Structure & Function

2. External – Reproductive Body

The function of your external genitals are to protect the internal parts from infection and allow sperm to enter our vagina.
Our vulva is the collective name for all our external genitals. A lot of people mistakenly use the term “vagina” to describe all female reproductive parts. However, your vagina is its own structure located inside your body.
The main parts of your vulva or external genitals are:

~ Labia majora:

Our labia majora (“large lips”) enclose and protect the other external reproductive organs.
During puberty, hair growth occurs on the skin of the labia majora, which also contain sweat and oil-secreting glands.

~ Labia minora:

Our labia minora (“small lips”) can have a variety of sizes and shapes.
They lie just inside your labia majora, and surround the opening to your vagina (the canal that joins the lower part of your uterus to the outside of your body) and urethra (the tube that carries pee from your bladder to the outside of your body).
This skin is very delicate and can become easily irritated and swollen.

~ Clitoris:

Our two labia minora meet at your clitoris, a small, sensitive protrusion that’s comparable to a penis.
Our clitoris is covered by a fold of skin called the prepuce and is very sensitive to stimulation.

~ Vaginal opening:

Our vaginal opening allows menstrual blood and babies to exit your body.
Tampons, fingers, sex toys or penises can go inside your vagina through your vaginal opening.

~ Hymen:

Our hymen is a piece of tissue covering or surrounding part of your vaginal opening.
It’s formed during development and present during birth.

~ Opening to Our urethra.

The opening to your urethra is the hole you pee from.
The urethra is part of your urinary system.
This system is made up of your kidneys, bladder, ureters and urethra.
Our kidneys clean your blood and produce urine, a waste product.
From your two kidneys, two ureters move the urine to the bladder, where it’s stored until you urinate (pee).

References:

Australian Government Department of Health and Aged Care, Healthdirect. Female reproductive system (https://www.healthdirect.gov.au/female-reproductive-system). Accessed 11/28/2022.
Merck Manual. Menstrual Cycle (https://www.merckmanuals.com/home/women-s-health-issues/biology-of-the-female-reproductive-system/menstrual-cycle). Accessed 11/28/2022.
Planned Parenthood. What are the parts of the female sexual anatomy? (https://www.plannedparenthood.org/learn/health-and-wellness/sexual-and-reproductive-anatomy/what-are-parts-female-sexual-anatomy) Accessed 11/28/2022.
The American College of Obstetricians and Gynecologists. Your Changing Body: Puberty in Girls (https://www.acog.org/Patients/FAQs/Your-Changing-Body-Puberty-in-Girls-Especially-for-Teens). Accessed 11/28/2022.
US Department of Health and Human Services, Office on Women’s Health. How the female reproductive system works (https://www.girlshealth.gov/body/reproductive/system.html). Accessed 11/28/2022.

January 12 2025

The Layers of the Hair Shaft

saeedurrahmangroup Anatomy Course 0

Introduction

The hair shaft is a critical structural component of human hair. It is visible above the skin surface and is composed of three distinct layers: Cuticle, Cortex, and Medulla. These layers are integral to the texture, strength, and overall health of hair.

Let’s delve into the anatomy and functions of these layers, their patterns, and their roles in maintaining healthy hair.

1. What is the Hair Shaft?

The hair shaft is the portion of hair visible above the skin’s surface. It is analogous to a pencil’s structure:

The outer colored layer of a pencil represents the cuticle.
The wooden part corresponds to the cortex.
The graphite center mirrors the medulla.

The hair shaft is composed of keratinized (dead) cells that serve aesthetic and protective functions.

2. Layers of the Hair Shaft

The hair shaft consists of three distinct layers, each contributing uniquely to hair’s characteristics.

a. Cuticle Layer

Description: The outermost transparent layer made of 5-10 thin, non-pigmented, keratinized cells arranged like roof tiles or fish scales.
Function:
- Shields the cortex and medulla from damage caused by chemicals, pollutants, or physical stress.
- Controls water content and moisture balance.
- Reflects light, giving hair a shiny appearance.
Patterns:
- Coronal (crown-like, in rodents and bats).
- Spinous (petal-like, in seals and cats).
- Imbricate (flattened scales, typical in humans).
Impact of Damage:
- Healthy Cuticle: Smooth with intact scales, making hair shiny and strong.
- Damaged Cuticle: Jagged with exposed inner layers, leading to dull, brittle, and frizzy hair.

b. Cortex Layer

Description: The thickest intermediate layer, accounting for 90% of the hair shaft. It lies beneath the cuticle and surrounds the medulla.
Structure:
- Composed of cortical cells connected by intercellular lipoproteins.
- Contains pigment granules that determine hair color (e.g., melanin for black color, absence of melanin for gray/white hair).
- Encloses macrofibrils and microfibrils made of keratin protein.
Functions:
- Provides hair strength, elasticity, and texture.
- Determines hair’s natural color and resilience.
Special Feature: The hydrogen bonds and disulfide bonds in keratin proteins give the hair its flexibility and tensile strength.

c. Medulla Layer

Description: The innermost core of the hair shaft, also called the medullary canal or pith.
Structure:
- Composed of loosely packed, transparent cells and air spaces.
- May be fragmented, continuous, or interrupted depending on hair type.
Presence:
- Typically found in thick or coarse hair.
- Absent in finer hair types.
Function:
- Provides minimal structural support.
- May influence the hair’s insulating properties.

3. Practical Demonstration

Activity: Observing the Hair Shaft Under a Microscope

Materials:
- Hair strands (different types: straight, curly, thick, fine).
- Microscope.
Procedure:
- Examine the outer layer (cuticle) for its scale-like pattern.
- Observe the cortex for pigmentation and fibril structures.
- Look for the presence or absence of the medulla in various hair types.

Observation:

Discuss how the differences in hair layers influence hair’s appearance and texture.

4. Discussion and FAQs

Why does damaged hair appear dull and frizzy?
- A damaged cuticle exposes the cortex, leading to moisture loss and rough texture.
What determines hair color?
- Melanin pigment in the cortex. Variations in its density and type (eumelanin for black/brown, pheomelanin for red) result in different hair colors.
Why is the medulla absent in fine hair?
- The medulla provides structural support in coarse hair, which is not as necessary for finer hair types.
How can we protect the cuticle layer?
- Avoid harsh chemicals, excessive heat, and rough brushing.
- Use conditioners to maintain moisture balance.

Conclusion

The hair shaft’s structure, particularly its layers (cuticle, cortex, and medulla), determines hair’s strength, texture, and appearance. A deeper understanding of these layers aids in maintaining healthy hair and identifying the causes of hair damage. By protecting the cuticle and supporting the cortex, we can enhance the overall health of our hair.

Would you like to explore hair follicle anatomy or the physiology of hair growth next?

July 30 2024

Anatomy Course

saeedurrahmangroup Anatomy Course, Blog 0

An anatomy course typically covers the following topics in detail:

### 1. **Introduction to Anatomy**
– **Definition and branches of anatomy**
– **Anatomical terminology**
– Directional terms (anterior, posterior, superior, inferior, etc.)
– Body planes (sagittal, coronal, transverse)
– Body cavities (cranial, thoracic, abdominal, pelvic)

### 2. **Cells and Tissues**
– **Cell structure and function**
– **Histology**
– Epithelial tissue
– Connective tissue
– Muscle tissue
– Nervous tissue

### 3. **Skeletal System**
– **Bone structure and function**
– **Classification of bones**
– Long, short, flat, irregular bones
– **The human skeleton**
– Axial skeleton (skull, vertebral column, rib cage)
– Appendicular skeleton (limbs, pectoral and pelvic girdles)
– **Joints and types of movement**
– Synovial, fibrous, cartilaginous joints

### 4. **Muscular System**
– **Types of muscle tissue**
– Skeletal, cardiac, smooth
– **Muscle anatomy**
– Muscle fibers, myofibrils, sarcomeres
– **Major muscle groups**
– Head and neck, upper limb, lower limb, torso
– **Muscle physiology**
– Mechanism of contraction, neuromuscular junction

### 5. **Nervous System**
– **Neuron structure and function**
– **Central nervous system**
– Brain (cerebrum, cerebellum, brainstem)
– Spinal cord
– **Peripheral nervous system**
– Cranial nerves, spinal nerves
– **Autonomic nervous system**
– Sympathetic and parasympathetic divisions

### 6. **Cardiovascular System**
– **Heart anatomy**
– Chambers, valves, major vessels
– **Blood vessels**
– Arteries, veins, capillaries
– **Blood flow and circulation**
– **Cardiac cycle and heart sounds**

### 7. **Respiratory System**
– **Anatomy of the respiratory tract**
– Nose, pharynx, larynx, trachea, bronchi, lungs
– **Mechanics of breathing**
– Inspiration, expiration
– **Gas exchange and transport**
– Alveoli, capillaries

### 8. **Digestive System**
– **Anatomy of the digestive tract**
– Mouth, esophagus, stomach, intestines
– **Accessory digestive organs**
– Liver, pancreas, gallbladder
– **Digestive processes**
– Ingestion, digestion, absorption, elimination

### 9. **Urinary System**
– **Kidney anatomy**
– Nephrons, renal cortex, renal medulla
– **Urinary tract**
– Ureters, bladder, urethra
– **Formation and excretion of urine**
– **Fluid and electrolyte balance**

### 10. **Reproductive System**
– **Male reproductive anatomy**
– Testes, vas deferens, seminal vesicles, prostate
– **Female reproductive anatomy**
– Ovaries, fallopian tubes, uterus, vagina
– **Gametogenesis**
– Spermatogenesis, oogenesis
– **Hormonal regulation**
– Menstrual cycle, pregnancy

### 11. **Endocrine System**
– **Major endocrine glands**
– Pituitary, thyroid, adrenal, pancreas
– **Hormones**
– Functions, mechanisms of action
– **Regulation of physiological processes**

### 12. **Lymphatic and Immune Systems**
– **Lymphatic system anatomy**
– Lymph nodes, lymphatic vessels, spleen, thymus
– **Immune system function**
– Innate and adaptive immunity
– **Immune cells**
– Lymphocytes, macrophages, dendritic cells

### 13. **Integumentary System**
– **Skin structure and function**
– Epidermis, dermis, hypodermis
– **Skin appendages**
– Hair, nails, glands (sebaceous, sweat)
– **Functions of the skin**
– Protection, thermoregulation, sensation

### 14. **Special Senses**
– **Vision**
– Eye anatomy, visual pathways
– **Hearing and balance**
– Ear anatomy, auditory pathways, vestibular system
– **Taste and smell**
– Tongue, olfactory system

These topics encompass the foundational elements of human anatomy, providing a comprehensive understanding of the body’s structure and function.