A&P exam 3

What does the sperm’s acrosome contain and how does this contribute to fertilization of the ovum?

·       The acrosome is a cap on the head of the sperm that contains special enzymes.

·       These enzymes help the sperm break through the outer layers of the ovum (egg). This allows the sperm to reach and fertilize the egg.

enzymes: Hyaluronidase – breaks down the cells surrounding the egg (the corona radiata).

• Acrosin – digests proteins in the zona pellucida, the protective glycoprotein layer around the egg.

What are the major functions of nurse cells?

“Nurse cells” in the testes help support and develop sperm cells. Their major functions are:

• nourish and protect developing sperm

• help sperm mature

• remove waste and damaged cells

• form the blood-testis barrier to protect sperm

• release hormones and chemicals that help control sperm production

These nurse cells are also called Sertoli cells.

Compare the number of chromosomes in primary spermatocytes and in spermatids. Do they have the same number of chromosomes?

No, they do not have the same number of chromosomes.

• Primary spermatocytes have 46 chromosomes (diploid, 2n).

• Spermatids have 23 chromosomes (haploid, n).

During meiosis, the chromosome number is cut in half so sperm cells can combine with the ovum during fertilization.

Describe the combined process of spermatogenesis and spermiogenesis and list the beginning and ending structures.

·      Spermatogenesis and Spermiogenesis

These are the processes that make mature sperm cells in the testes.

• Spermatogenesis = production of sperm cells through cell division

• Spermiogenesis = final maturation of the sperm cells

The process begins with spermatogonia (stem cells).
These develop into:

1. primary spermatocytes

2. secondary spermatocytes

3. spermatids

Then during spermiogenesis, the spermatids change shape and become spermatozoa (mature sperm cells).

Beginning structure:

• Spermatogonia

Ending structure:

• Spermatozoa (mature sperm)

What is spermiogenesis and what is the result of this process?

Spermiogenesis

Spermiogenesis is the final stage of sperm development where spermatids change into mature sperm cells.

During this process:

• the sperm grows a tail,

• forms an acrosome on the head,

• and loses extra cytoplasm.

Result:

The result is a mature sperm cell (spermatozoon) that can move and fertilize an ovum.

What is the haploid (n) result of meiosis I?

The haploid (n) result of meiosis I is two secondary spermatocytes, each containing 23 chromosomes.

At what stage does a developing sperm cell begin to grow a tail?

·       A developing sperm cell begins to grow a tail during spermiogenesis, when the spermatid starts changing into a mature sperm cell.

What is the most important role of meiosis in sexual reproduction?

·      The most important role of meiosis in sexual reproduction is to reduce the chromosome number by half.

·      This creates haploid sex cells (sperm and eggs) with 23 chromosomes so that when fertilization happens, the offspring has the normal diploid number of 46 chromosomes.

·      Meiosis also increases genetic variation between offspring.

describe the composition of semen and functions of its components.

Composition of Semen and Functions of Its Components

Semen is made of:

• sperm cells

• fluids from the male reproductive glands

Main components include:

• Sperm – fertilizes the ovum

• Seminal vesicle fluid – provides fructose (sugar) for energy and helps sperm move

• Prostate gland fluid – helps activate and protect sperm

• Bulbourethral gland fluid – lubricates and neutralizes acidity in the urethra

Together, these fluids nourish, protect, and help transport sperm.

describe the sequence of cell types in spermatogenesis, and relate these to the stages of meiosis

Sequence of Cell Types in Spermatogenesis

1. Spermatogonia

   • stem cells in the testes

   • divide by mitosis to make more cells

2. Primary spermatocytes

   • formed from spermatogonia

   • enter meiosis I

   • have 46 chromosomes

3. Secondary spermatocytes

   • produced after meiosis I

   • enter meiosis II

   • have 23 chromosomes

4. Spermatids

   • produced after meiosis II

   • haploid cells with 23 chromosomes

5. Spermatozoa (mature sperm)

   • formed during spermiogenesis when spermatids mature and grow tails

Relation to Meiosis

• Meiosis I: primary spermatocyte → secondary spermatocytes

• Meiosis II: secondary spermatocytes → spermatids

describe the stages of meiosis and contrast meiosis with mitosis

Stages of Meiosis

Meiosis I

1. Prophase I – chromosomes pair up and exchange genetic material

2. Metaphase I – chromosome pairs line up in the middle

3. Anaphase I – chromosome pairs separate

4. Telophase I & Cytokinesis – two cells form

Meiosis II

1. Prophase II – chromosomes prepare to divide again

2. Metaphase II – chromosomes line up in the middle

3. Anaphase II – sister chromatids separate

4. Telophase II & Cytokinesis – four haploid cells form

Which hormone(s) directly stimulate(s) the development of male secondary sex characteristics?

The hormone that directly stimulates the development of male secondary sex characteristics is testosterone.

Testosterone causes traits such as:

·       deeper voice,

·       facial and body hair,

·       increased muscle mass,

·       and male body shape development.

What is an androgen? Provide example(s) of androgen(s)

An androgen is a male sex hormone that helps develop and maintain male reproductive structures and male secondary sex characteristics.

Examples of androgens include:

·       Testosterone (the main androgen)

·       Dihydrotestosterone (DHT)

·       Androstenedione

What hormone suppresses spermatogenesis without affecting testosterone secretion?

·       The hormone that suppresses spermatogenesis without affecting testosterone secretion is inhibin.        

·       Inhibin is released by the Sertoli (nurse) cells and decreases FSH secretion, which slows sperm production.

What is the difference between spermiogenesis and spermatogenesis?

·       Spermatogenesis is the entire process of producing sperm cells, starting with spermatogonia and ending with spermatids. It includes cell division through meiosis.

·       Spermiogenesis is the final step where spermatids mature and change into fully formed sperm cells with tails.

What is an androgen? What cell(s) do NOT have andogen receptors, and consequently do not respond to androgens?

An androgen is a male sex hormone that promotes male reproductive functions and male secondary sex characteristics.
Examples include:

• Testosterone

• Dihydrotestosterone (DHT)

Cells that do not have androgen receptors and therefore do not respond to androgens are Sertoli (nurse) cells before puberty and some developing sperm cells.

What hormones are inhibited by testosterone?

Testosterone inhibits the release of:

• GnRH (gonadotropin-releasing hormone) from the hypothalamus

• LH (luteinizing hormone) from the anterior pituitary

This negative feedback helps regulate testosterone levels in the body.

When do the testes start secreting testosterone?

·      The testes begin secreting significant amounts of testosterone at puberty.

·      This happens when LH from the pituitary gland stimulates the interstitial (Leydig) cells in the testes.

describe the hormonal control of puberty; describe the resulting changes in the male body; and define and describe male climacteric and the effect of aging on male reproductive function.

·      Hormonal Control of Puberty

Puberty begins when the hypothalamus releases GnRH (gonadotropin-releasing hormone).
GnRH stimulates the pituitary gland to release:

• LH (luteinizing hormone)

• FSH (follicle-stimulating hormone)

LH causes the testes to produce testosterone, while FSH helps stimulate sperm production.

b. Changes in the Male Body During Puberty

Increased testosterone causes:

• growth of the penis and testes

• sperm production to begin

• deeper voice

• facial, pubic, and body hair growth

• increased muscle and bone growth

• increased sex drive

c. Male Climacteric and Aging Effects

Male climacteric is the gradual decline in testosterone levels as men age.

Effects may include:

• lower sex drive

• decreased sperm production

• erectile difficulties

• loss of muscle mass and strength

• fatigue and mood changes

Unlike female menopause, male reproductive ability usually does not stop completely.

How does an enlarged prostate affect urination? Explain

·      An enlarged prostate can make urination difficult because the prostate surrounds the urethra just below the bladder.

When the prostate enlarges, it squeezes the urethra, which can:

·       weaken urine flow,

·       make it hard to start urinating,

·       cause frequent urination,

·       and prevent the bladder from fully emptying.

Which sexual organs are paired, and which ones are not paired (i.e., men only have one)?

Which sexual organs are paired, and which ones are not paired (i.e., men only have one)?

·      Paired Male Sexual Organs

Men have two of each of these:

• testes

• epididymides

• ductus (vas) deferens

• seminal vesicles

• bulbourethral glands

Unpaired Male Sexual Organs

Men only have one of these:

• penis

• prostate gland

• urethra

• scrotum

Describe the anatomical structure and the location of the prostate gland with respect to the urinary bladder and urethra.

·       The prostate gland is a walnut-sized gland located directly below the urinary bladder. It surrounds the first part of the urethra, called the prostatic urethra.

·       Because the urethra passes through the prostate, enlargement of the gland can affect urine flow.

What gland produces most of the semen?

·       The seminal vesicles produce most of the semen.

·       They make a fluid rich in fructose that provides energy for sperm.

What is the correct pathway of sperms from their formation to ejaculation?

The pathway of sperm is:

1. Seminiferous tubules (where sperm are made)

2. Epididymis (sperm mature and are stored)

3. Ductus/Vas deferens

4. Ejaculatory duct

5. Urethra

6. Out through the penis during ejaculation

What are the major functions of the epididymis and how does this structure relate to sperm maturation?

The major functions of the epididymis are to:

• store sperm,

• allow sperm to mature,

• and transport sperm to the ductus (vas) deferens.

As sperm move through the epididymis, they mature and gain the ability to swim and fertilize an ovum.

What is/are the major function(s) of the blood-testis barrier?

The major functions of the blood-testis barrier are to:

·       protect developing sperm from harmful substances in the blood,

·       prevent the immune system from attacking sperm cells,

·       and help maintain a stable environment for sperm development.

describe the blood and nerve supply to the penis; and explain how these govern erection and ejaculation.

·      Blood Supply to the Penis

The penis gets blood from arteries that branch off the internal pudendal artery.

• Deep arteries fill the penis with blood during an erection

• Dorsal arteries supply the skin and tip of the penis

• Veins carry blood back out afterward

Nerve Supply to the Penis

The penis has nerves for feeling and for controlling erection and ejaculation.

• Sensory nerves let you feel touch

• Parasympathetic nerves cause an erection

• Sympathetic nerves cause ejaculation

Erection

When a person is sexually stimulated:

• parasympathetic nerves relax the arteries,

• more blood flows into the penis,

• blood gets trapped there,

• and the penis becomes erect.

Ejaculation

During ejaculation:

• sympathetic nerves make muscles squeeze,

• semen moves through the urethra and out of the body,

• then blood leaves the penis and the erection goes away.

Describe the anatomy, location, and major function of the pampiniform plexus of veins as it relates to temperature regulation.

·    The pampiniform plexus is a network of veins located in the spermatic cord around the testicular artery above the testes.

·       Its major function is temperature regulation. The cooler venous blood in the plexus cools the warmer arterial blood before it reaches the testes. This helps keep the testes slightly cooler than body temperature, which is important for normal sperm production.

How does the cremaster function to maintain an optimal temperature for the testes?

The cremaster muscle helps maintain the proper temperature of the testes by moving them closer to or farther from the body.

• When it is cold, the cremaster contracts and pulls the testes closer to the body for warmth.

• When it is warm, the muscle relaxes and allows the testes to hang farther away to cool down.

This helps keep the testes at the best temperature for sperm production.

Describe the anatomical locations and functions of the corpus spongiosum and the corpus cavernosum.

Corpus Cavernosum

• Two columns of erectile tissue located on the upper (dorsal) side of the penis

• Main function: fill with blood during sexual arousal to produce an erection

Corpus Spongiosum

• Single column of erectile tissue located on the underside of the penis around the urethra

• Main function: keeps the urethra open during erection so semen and urine can pass through

describe the anatomy of the scrotum, testes, and penis

·      Anatomy of the Scrotum, Testes, and Penis

Scrotum

• A pouch of skin and muscle that holds the testes outside the body

• Helps regulate temperature for sperm production

Testes

• Male reproductive organs located inside the scrotum

• Produce sperm and testosterone

• Contain seminiferous tubules where sperm are formed

Penis

• External male reproductive organ used for urination and ejaculation

• Contains:

  • two corpora cavernosa

  • one corpus spongiosum surrounding the urethra

describe the pathway taken by a sperm cell from its formation to its ejaculation, naming all the passages it travels

·      Pathway of a Sperm Cell

1. Seminiferous tubules

2. Rete testis

3. Efferent ductules

4. Epididymis

5. Ductus (vas) deferens

6. Ejaculatory duct

7. Urethra

8. Out through the penis

state the names, locations, and functions of the male accessory reproductive glands.

Male Accessory Reproductive Glands

Seminal Vesicles

• Located behind the urinary bladder

• Produce most of the semen and provide fructose for sperm energy

Prostate Gland

• Located below the bladder and around the urethra

• Produces fluid that activates and protects sperm

Bulbourethral (Cowper’s) Glands

• Located below the prostate near the urethra

• Produce lubricating fluid that neutralizes acidity in the urethra

What are the secondary sex organs of males and females?

Male Secondary Sex Organs

• epididymis

• ductus (vas) deferens

• seminal vesicles

• prostate gland

• bulbourethral glands

• penis

• scrotum

• urethra

Female Secondary Sex Organs

• uterine tubes (fallopian tubes)

• uterus

• vagina

• mammary glands

• external genitalia (vulva)

These organs support reproduction but do not directly produce gametes (sperm or ova).

What are the primary sex organs of males and females?

Primary Sex Organs

·       Male: testes

·       Female: ovaries

Identify the gonad and gamete of the male.

·       Gonad of the male: testes

·       Gamete of the male: sperm (sperm cell or spermatozoon) 

explain the neurological control of defecation.

What stimulates defecation?

Defecation is controlled by reflexes involving the spinal cord and the autonomic nervous system.

When feces enter and stretch the rectum, stretch receptors are stimulated. This sends nerve signals to the spinal cord, which triggers the defecation reflex.

The reflex causes:

• contraction of the rectum,

• relaxation of the internal anal sphincter,

• and the urge to defecate.

Defecation is stimulated mainly by stretching of the rectal walls as feces fill the rectum. Voluntary relaxation of the external anal sphincter allows defecation to occur.

discuss the types of contractions that occur in the colon

The colon has two main types of contractions:

1. Haustral contractions

• slow segmenting movements

• mix and move feces slowly through the colon

• help with water and electrolyte absorption

2. Mass movements

• strong waves of contraction that move feces long distances toward the rectum

• often occur after eating due to the gastrocolic reflex

• help trigger defecation

 

state the physiological significance of intestinal bacteria

Intestinal bacteria are important because they:

·       help digest certain foods, especially fiber

·       produce vitamins such as vitamin K and some B vitamins

·       help protect against harmful bacteria

·       support normal immune system function

·       help maintain a healthy intestinal environment

contrast the mucosa of the colon with that of the small intestine

Small Intestine Mucosa

• Has villi and microvilli to greatly increase surface area for nutrient absorption

• Contains folds for digestion and absorption

Colon Mucosa

• Does not have villi

• Contains many mucus-producing goblet cells

• Mainly functions in water absorption and feces formation rather than nutrient absorption

identify the most fundamental biological distinction between male and female

Most Fundamental Biological Distinction Between Male and Female

The most basic biological difference is the type of gametes produced:

• Males produce small, motile sperm

• Females produce large, nonmotile ova (eggs)

explain the role of the sex chromosomes in determining sex

Role of the Sex Chromosomes in Determining Sex

• Females usually have XX chromosomes

• Males usually have XY chromosomes

The sperm determines the sex of the offspring:

• X sperm + X egg = XX (female)

• Y sperm + X egg = XY (male)

explain how the Y chromosome determines the response of the fetal gonad to prenatal hormones

Role of the Sex Chromosomes in Determining Sex

• Females usually have XX chromosomes

• Males usually have XY chromosomes

The sperm determines the sex of the offspring:

• X sperm + X egg = XX (female)

• Y sperm + X egg = XY (male)

identify which of the male and female external genitalia are homologous to each other

Homologous Male and Female External Genitalia

Structures that develop from the same embryonic tissues are homologous:

• Penis ↔ Clitoris

• Scrotum ↔ Labia majora

describe the descent of the gonads and explain why it is important.

Descent of the Gonads and Its Importance

• Testes develop in the abdominal cavity before birth

• They descend into the scrotum through the inguinal canal

This is important because sperm production requires a temperature slightly lower than normal body temperature. The scrotum keeps the testes cooler for normal sperm development.

describe the gross anatomy of the large intestine

The large intestine begins at the cecum, which is attached to the appendix. It then continues through the:

• ascending colon

• transverse colon

• descending colon

• sigmoid colon

• rectum

• anal canal

The large intestine is wider and shorter than the small intestine and contains pouch-like sections called haustra.

summarize the functions of the large intestine

Functions of the Large Intestine

The large intestine:

• absorbs water and electrolytes,

• forms and stores feces,

• houses intestinal bacteria,

• absorbs vitamins made by bacteria (such as vitamin K),

• and eliminates waste through defecation.

Where are fatty acids absorbed?

·      Fatty acids are absorbed mainly in the small intestine, especially through the microvilli of the intestinal villi.

·      Most fatty acids enter the lacteals (lymphatic capillaries) before eventually reaching the bloodstream.

Where are monosaccharides absorbed?

·      Monosaccharides are absorbed in the small intestine, mainly through the microvilli of the intestinal villi.

·      They enter the blood capillaries and are transported to the liver through the hepatic portal vein.

Where are amino acids are absorbed?

·      Amino acids are absorbed in the small intestine, mainly through the microvilli of the intestinal villi.

·      They enter the blood capillaries and travel to the liver through the hepatic portal vein.

Mechanical Digestion

Mechanical digestion is the physical breakdown of food into smaller pieces. It does not change the chemical makeup of the food.

Examples:

• chewing

• churning in the stomach

• segmentation in the intestines

Chemical Digestion

Chemical digestion breaks food molecules into smaller nutrients using enzymes and acids.

Examples:

• salivary amylase breaking down starch

• pepsin digesting proteins

• pancreatic lipase digesting fats

identify the basic chemical process that underlies all chemical digestion, and name the major substrates and products of this process

·       The basic chemical process underlying all chemical digestion is hydrolysis.

Hydrolysis uses water to break large food molecules into smaller molecules.

Major substrates and products:

• Carbohydrates → monosaccharides

• Proteins → amino acids

• Fats (lipids) → fatty acids and monoglycerides/glycerol

list the regions of the digestive tract and the accessory organs of the digestive system

Regions of the Digestive Tract

1. Mouth (oral cavity)

2. Pharynx

3. Esophagus

4. Stomach

5. Small intestine

   • duodenum

   • jejunum

   • ileum

6. Large intestine

   • cecum

   • colon

   • rectum

   • anal canal

Accessory Organs of the Digestive System

• Teeth

• Tongue

• Salivary glands

• Liver

• Gallbladder

• Pancreas

identify the layers of the digestive tract and describe its relationship to the peritoneum

Layers of the Digestive Tract

From the inside outward, the digestive tract consists of four layers:

1. Mucosa – innermost layer; functions in secretion, absorption, and protection.

   • Epithelium

   • Lamina propria

   • Muscularis mucosae

2. Submucosa – contains blood vessels, lymphatic vessels, glands, and the submucosal (Meissner) plexus.

3. Muscularis Externa – responsible for mixing and propelling food.

   • Inner circular layer

   • Outer longitudinal layer

   • Contains the myenteric (Auerbach) plexus between the muscle layers.

4. Serosa (or Adventitia) – outermost layer.

   • Serosa covers intraperitoneal organs and is the visceral peritoneum.

   • Adventitia anchors retroperitoneal organs to surrounding tissues.

Relationship to the Peritoneum

The peritoneum is a serous membrane of the abdominal cavity.

• Parietal peritoneum lines the abdominal wall.

• Visceral peritoneum covers abdominal organs (this is the serosa).

• The space between them contains peritoneal fluid, which reduces friction.

• Mesenteries are double layers of peritoneum that suspend digestive organs and carry blood vessels, nerves, and lymphatics.

describe the general neural and control over digestive function.

General Neural Control of Digestive Function

Digestive activity is regulated by the nervous system:

• Enteric Nervous System (ENS) – intrinsic “brain of the gut.”

  • Myenteric plexus: controls motility.

  • Submucosal plexus: controls secretion and blood flow.

• Parasympathetic Nervous System

  • Stimulates digestion.

  • Increases motility and secretions.

• Sympathetic Nervous System

  • Inhibits digestion.

  • Decreases motility and secretions and constricts blood vessels.

describe the chemical controls over digestive function.

General Chemical (Hormonal) Control of Digestive Function

Hormones released by the digestive tract help regulate digestion:

• Gastrin – stimulates stomach acid secretion and motility.

• Secretin – stimulates bicarbonate secretion from the pancreas and inhibits stomach activity.

• Cholecystokinin (CCK) – stimulates enzyme release from the pancreas and bile release from the gallbladder; slows stomach emptying.

• GIP (Glucose-dependent insulinotropic peptide) – inhibits gastric activity and stimulates insulin release.

Simple summary: The digestive tract has four layers (mucosa, submucosa, muscularis externa, and serosa/adventitia). Digestion is controlled by the enteric nervous system, autonomic nerves, and hormones that regulate secretion, absorption, blood flow, and movement of food.

list the functions and major physiological processes of the digestive system

The digestive system’s main function is to break down food, absorb nutrients and water, and eliminate waste.

Major Physiological Processes

1. Ingestion

   • Taking food and liquids into the mouth.

2. Secretion

   • Release of saliva, digestive enzymes, acid, bile, mucus, and hormones.

3. Mechanical Digestion

   • Physical breakdown of food by chewing, churning, and segmentation.

4. Chemical Digestion

   • Breakdown of food molecules by enzymes into absorbable nutrients.

5. Motility

   • Movement of food through the digestive tract.

   • Includes swallowing, peristalsis, and segmentation.

6. Absorption

   • Movement of nutrients, water, vitamins, and minerals from the digestive tract into the blood or lymph.

7. Compaction

   • Absorption of water and formation of feces in the large intestine.

8. Defecation

   • Elimination of indigestible waste from the body.

Simple Summary

The digestive system ingests food, secretes digestive juices, mechanically and chemically digests food, moves it through the tract, absorbs nutrients and water, compacts waste, and eliminates feces.

What is the uptake of nutrient molecules into the body’s own tissues?

The uptake of nutrient molecules into the body’s own tissues is called absorption.

Absorption is the movement of digested nutrients from the digestive tract into the blood or lymph, where they can be transported to the body’s cells and tissues for use

Functions of Saliva

1. Moistens and lubricates food for easier swallowing.

2. Forms a bolus that can be swallowed.

3. Begins carbohydrate digestion through salivary amylase.

4. Begins lipid digestion through lingual lipase.

5. Dissolves food chemicals so taste receptors can detect them.

6. Cleanses the mouth and helps prevent infections.

7. Buffers acids and helps protect teeth from decay

Composition of Saliva

Saliva is about 99.5% water and 0.5% dissolved substances, including:

• Water – moistens food and dissolves chemicals for taste.

• Mucus (mucin) – lubricates food and helps form a bolus for swallowing.

• Salivary amylase – begins carbohydrate digestion.

• Lingual lipase – begins fat digestion.

• Electrolytes – sodium, potassium, chloride, bicarbonate, and phosphate ions.

• Lysozyme and antibodies (IgA) – help kill bacteria and protect against infection.

Where does carbohydrate digestion begin?

Carbohydrate Digestion

• Begins in the mouth

• Enzyme: Salivary amylase

• Function: Breaks starch into smaller carbohydrate molecules.

Where does carbohydrate digestion begin?

Carbohydrate Digestion

• Begins in the mouth

• Enzyme: Salivary amylase

• Function: Breaks starch into smaller carbohydrate molecules.

Where does lipid digestion begin?

Lipid (Fat) Digestion

• Begins in the mouth and stomach, but most digestion occurs in the small intestine.

• Mouth: Lingual lipase starts fat digestion.

• Stomach: Gastric lipase continues fat digestion.

• Small intestine: Pancreatic lipase performs the majority of fat digestion after bile emulsifies the fats.

describe the neural control of salivation and swallowing.

• Salivation: Controlled mainly by the parasympathetic nervous system through salivatory nuclei in the medulla.

• Swallowing center: Located in the medulla oblongata.

• Swallowing phases: Voluntary oral phase → involuntary pharyngeal phase → involuntary esophageal phase.

• Peristalsis moves food from the esophagus to the stomach.

Where is the swallowing center is located?

The swallowing center is located in the medulla oblongata of the brainstem.

It coordinates the muscles involved in swallowing and receives sensory input from the mouth, pharynx, and esophagus. Once swallowing is initiated, the swallowing center automatically controls the sequence of events that move food from the mouth to the stomach.

Gross Anatomy of the Stomach

The stomach is a J-shaped organ located between the esophagus and the small intestine.

Regions of the stomach:

1. Cardia – Area where the esophagus enters the stomach.

2. Fundus – Dome-shaped superior portion that stores food and gas.

3. Body – Largest central region; main site of mixing and digestion.

4. Pylorus – Lower region that empties into the duodenum.

   • Includes the pyloric antrum, pyloric canal, and pyloric sphincter.

Other features:

• Lesser curvature – Shorter, medial border.

• Greater curvature – Longer, lateral border.

• Rugae – Folds in the stomach lining that allow expansion when the stomach fills.

Microscopic Anatomy of the Stomach

The stomach wall has the same four basic layers as the rest of the digestive tract:

1. Mucosa

   • Contains gastric pits that lead to gastric glands.

   • Houses the epithelial cells that produce stomach secretions.

2. Submucosa

   • Connective tissue containing blood vessels, lymphatic vessels, and nerves.

3. Muscularis externa

   • Has three layers of smooth muscle:

     • Inner oblique layer

     • Middle circular layer

     • Outer longitudinal layer

   • These layers churn and mix food.

4. Serosa

   • Outer visceral peritoneum covering the stomach.

state the function of each type of epithelial cell in the gastric mucosa

• Surface mucous cells → Protection

• Mucous neck cells → Lubrication

• Parietal cells → HCl + Intrinsic Factor

• Chief cells → Pepsinogen + Gastric Lipase

• Enteroendocrine cells → Hormones (especially Gastrin)

identify the secretions of the stomach and state their functions

• Mucus → protects stomach

• HCl → activates pepsin, kills bacteria, denatures proteins

• Intrinsic factor → helps absorb vitamin B₁₂

• Pepsinogen/Pepsin → digests proteins

• Gastric lipase → digests fats

• Gastrin → increases acid secretion and stomach activity

• Histamine → stimulates acid secretion

• Ghrelin → increases hunger sensation

explain how the stomach produces hydrochloric acid and pepsin

How the Stomach Produces Hydrochloric Acid (HCl)

Parietal cells in the gastric glands produce HCl:

1. Inside the parietal cell, water (H₂O) and carbon dioxide (CO₂) combine.

2. The enzyme carbonic anhydrase converts them into carbonic acid (H₂CO₃).

3. Carbonic acid breaks down into hydrogen ions (H⁺) and bicarbonate ions (HCO₃⁻).

4. The H⁺ ions are pumped into the stomach lumen by proton pumps.

5. Chloride ions (Cl⁻) diffuse into the stomach lumen through channels.

6. H⁺ and Cl⁻ combine in the stomach lumen to form hydrochloric acid (HCl).

How the Stomach Produces Pepsin

Chief cells produce pepsinogen, an inactive enzyme precursor (zymogen).

1. Chief cells secrete pepsinogen into the stomach.

2. HCl from parietal cells converts pepsinogen into pepsin.

3. Once some pepsin is present, it can activate additional pepsinogen molecules.

4. Pepsin begins the digestion of proteins into smaller peptides.

Quick Summary

• Parietal cells → HCl

• Chief cells → Pepsinogen

• HCl activates pepsinogen → Pepsin

• Pepsin digests proteins into smaller fragments.

describe the contractile responses of the stomach to food

When food enters the stomach, the stomach responds with several types of contractions:

1. Receptive relaxation – The upper stomach (fundus) relaxes and stretches to accommodate incoming food without a large increase in pressure.

2. Peristaltic mixing waves – Gentle contractions begin in the body of the stomach and move toward the pylorus. These waves mix food with gastric juices, forming chyme.

3. Antral pumping – Strong contractions in the antrum (lower stomach) force chyme toward the pyloric sphincter.

4. Retropulsion – Because the pyloric sphincter is mostly closed, most of the chyme is pushed back into the stomach. This action thoroughly mixes and mechanically breaks down food.

5. Gastric emptying – Small amounts of chyme are allowed to pass through the pyloric sphincter into the duodenum at a controlled rate.

In summary:

The stomach first stores food, then mixes and churns it with gastric juices, and finally slowly releases chyme into the small intestine for further digestion.

What cell secretes pepsinogen? What activates pepsinogen and what cells secrete the substance that activates this substance?

• What cell secretes pepsinogen?
  Chief cells of the gastric glands secrete pepsinogen.

• What activates pepsinogen?
  Hydrochloric acid (HCl) activates pepsinogen, converting it into pepsin.

• What cells secrete the substance that activates pepsinogen?
  Parietal cells secrete hydrochloric acid (HCl)

identify the secretions of the stomach and state their functions

The stomach secretes:

• HCl → activates pepsin and kills germs.

• Pepsinogen/Pepsin → digests proteins.

• Gastric lipase → digests some fats.

• Mucus and bicarbonate → protect the stomach lining.

• Intrinsic factor → helps absorb vitamin B₁₂.

What is a zymogen?

A zymogen is an inactive precursor of an enzyme. It must be activated before it can perform its digestive function.

What is the zymogen of pepsin?

The zymogen of pepsin is pepsinogen.

Why is pepsin first secreted as a zymogen?

Pepsin is a powerful protein-digesting enzyme. If it were released in its active form, it could digest the proteins of the cells that produce it and damage the stomach lining. By being secreted as inactive pepsinogen, it is safe until it reaches the stomach lumen, where hydrochloric acid (HCl) activates it to pepsin.

Simple Answer

• Zymogen: an inactive enzyme precursor.

• Pepsin’s zymogen: pepsinogen.

• Reason: to prevent the enzyme from digesting the stomach’s own cells before it reaches the stomach lumen.

explain how the stomach produces hydrochloric acid and pepsin

    * Parietal cells produce HCl by secreting hydrogen and chloride ions into the stomach.

* Chief cells secrete pepsinogen.

* HCl activates pepsinogen, converting it into pepsin, which digests proteins.

What is the ideal pH for the enzyme pepsin?

• Ideal pH for pepsin: 1.5–2.0 (very acidic, found in the stomach)

What is the ideal pH for the enzyme, pancreatic amylase?

• Ideal pH for pancreatic amylase: about 7.0–8.0 (neutral to slightly alkaline, found in the small intestine)

Which enzyme functions at the lowest pH?

Pepsin

Pepsin works best in the highly acidic environment of the stomach, while pancreatic amylase requires the more alkaline environment of the small intestine.

Answer: Pepsin functions at the lowest pH.

describe the three phases of gastric function

1. Cephalic Phase

Before food enters the stomach

• Triggered by the sight, smell, taste, or thought of food.

• The parasympathetic nervous system (vagus nerve) stimulates gastric glands.

• Increases secretion of HCl, enzymes, and mucus.

2. Gastric Phase

When food enters the stomach

• Triggered by stomach distension and the presence of proteins.

• Stretch receptors and rising pH stimulate gastric activity.

• The hormone Gastrin is released.

• Increases gastric secretions and stomach motility.

• This is the phase responsible for most gastric digestion.

3. Intestinal Phase

When chyme enters the small intestine

• Initially causes a brief stimulation of the stomach.

• Then mainly inhibits gastric activity through the enterogastric reflex and intestinal hormones.

• Slows gastric emptying and reduces gastric secretions.

How Gastric Activity is Activated

• Sight, smell, taste, or thought of food (cephalic phase)

• Stomach distension

• Proteins and peptides in the stomach

• Parasympathetic stimulation (vagus nerve)

• Release of gastrin

How Gastric Activity is Inhibited

• Chyme entering the duodenum

• Excess acidity in the small intestine

• Fats in the duodenum

• Stretching of the duodenum

• Enterogastric reflex

• Hormones such as Secretin, Cholecystokinin (CCK), and Glucose-dependent insulinotropic peptide

Quick Summary

• Cephalic phase: food is anticipated → stomach prepares.

• Gastric phase: food is in the stomach → digestion is stimulated.

• Intestinal phase: chyme enters the small intestine → stomach activity is slowed to allow intestinal digestion and absorption.

 

How does the enterogastric reflex affect gastric motility when there is chyme in the small intestine? Why does this reflex affect the stomach in this way?

The enterogastric reflex slows the stomach through both nervous and hormonal mechanisms:

1. Nervous mechanism

   • When chyme enters the duodenum, receptors detect stretching, acidity, fats, and high osmolarity.

   • Nerve signals are sent through the enteric nervous system and the autonomic nervous system.

   • These signals inhibit the stomach’s smooth muscle contractions and reduce gastric emptying.

2. Hormonal mechanism

   • The duodenum releases hormones such as Secretin, Cholecystokinin (CCK), and Glucose-dependent insulinotropic peptide (GIP).

   • These hormones travel through the bloodstream to the stomach and decrease gastric motility and secretion.

In short: When chyme enters the small intestine, nerves and hormones send “slow down” signals to the stomach, reducing its contractions and delaying gastric emptying so the small intestine can keep up with digestion.

describe the gross and microscopic anatomy of the liver

Liver

Gross Anatomy

• Largest internal organ in the body.

• Located in the right upper abdomen beneath the diaphragm.

• Divided into right and left lobes (plus smaller caudate and quadrate lobes).

• Receives blood from the hepatic artery and hepatic portal vein.

Microscopic Anatomy

• Made up of hepatic lobules, which are hexagonal units.

• Lobules contain:

  • Hepatocytes (liver cells)

  • Sinusoids (specialized capillaries)

  • A central vein

  • Portal triads (branch of hepatic artery, portal vein, and bile duct)

describe the gross and microscopic anatomy of the gallbladder

Gallbladder

Gross Anatomy

• Small, pear-shaped sac located on the underside of the liver.

• Stores and concentrates bile.

• Connected to the biliary system by the cystic duct.

Microscopic Anatomy

• Lined with simple columnar epithelium with microvilli.

• Mucosa is highly folded to increase surface area for water absorption.

• Lacks a submucosa.

• Contains smooth muscle that contracts to expel bile.

describe the gross and microscopic anatomy of the bile duct system

Bile Duct System

Gross Anatomy

Bile flows through the following pathway:

1. Bile canaliculi

2. Small bile ducts

3. Right and left hepatic ducts

4. Common hepatic duct

5. Cystic duct (to and from gallbladder)

6. Common bile duct

7. Duodenum

Microscopic Anatomy

• Ducts are lined by epithelial cells that transport bile.

• Larger ducts have connective tissue and smooth muscle in their walls.

describe the gross and microscopic anatomy of the pancreas

Pancreas

Gross Anatomy

• Retroperitoneal organ located behind the stomach.

• Divided into:

  • Head

  • Body

  • Tail

• Connected to the duodenum by the pancreatic duct.

Microscopic Anatomy

The pancreas has two functional parts:

Exocrine Pancreas

• Made of acinar cells arranged in clusters called acini.

• Produces digestive enzymes and bicarbonate-rich fluid.

• Secretions travel through ducts to the duodenum.

Endocrine Pancreas

• Consists of pancreatic islets (Islets of Langerhans).

• Produces hormones such as:

  • Insulin

  • Glucagon

Quick Summary

• Liver: composed of hepatic lobules with hepatocytes, sinusoids, and portal triads; produces bile.

• Gallbladder: stores and concentrates bile; lined with folded simple columnar epithelium.

• Bile ducts: transport bile from the liver and gallbladder to the duodenum.

• Pancreas: exocrine acini produce digestive enzymes; endocrine islets produce hormones.

 

Where does contact digestion occur? 

·      Contact digestion occurs at the brush border of the small intestine on the microvilli of the intestinal cells.

·      It involves enzymes attached to the cell membrane that complete the final steps of digestion.

Define contact digestion. 

·      Contact digestion is the final stage of chemical digestion that occurs when nutrients come into contact with enzymes attached to the brush border (microvilli) of the small intestine.

What nutrient is absorbed by the lacteals of the small intestine?

·      The lacteals of the small intestine absorb fatty acids and other lipids (fats).

What regulates digestive tract motility, secretion, and blood flow? In what digestive tract layers are the parts of this plexus found?

The Enteric Nervous System (ENS) regulates digestive tract motility, secretion, and blood flow.

The ENS consists of two major nerve plexuses:

1. Myenteric (Auerbach’s) Plexus

   • Located between the circular and longitudinal layers of the muscularis externa.

   • Primarily regulates motility (muscle contractions and peristalsis).

2. Submucosal (Meissner’s) Plexus

   • Located in the submucosa.

   • Primarily regulates secretion, absorption, and local blood flow.

Quick Exam Answer

• What regulates digestive tract motility, secretion, and blood flow?

  • The Enteric Nervous System (ENS).

• Where are its plexuses found?

  • Myenteric plexus: Between the circular and longitudinal layers of the muscularis externa.

What organ synthesizes bile acids? How are bile acids formed? What must first be metabolized for bile acids to be formed? 

• What organ synthesizes bile acids?
  The liver synthesizes bile acids.

• How are bile acids formed?
  Bile acids are formed when liver cells chemically modify cholesterol through a series of enzymatic reactions.

• What must first be metabolized for bile acids to be formed?
  Cholesterol must be metabolized. The liver converts cholesterol into primary bile acids, which are then secreted into bile.

Simple Answer

The liver makes bile acids by breaking down and modifying cholesterol. Therefore, cholesterol must be metabolized first for bile acids to be formed.

explain how hormones regulate secretion by the liver and pancreas

Hormones released by the small intestine help regulate secretions from the liver and pancreas:

• Secretin is released when acidic chyme enters the duodenum. It stimulates the pancreas to secrete bicarbonate-rich fluid to neutralize the acid and stimulates the liver to produce more bile.

• Cholecystokinin (CCK) is released in response to fats and proteins in the small intestine. It stimulates the pancreas to release digestive enzymes and causes the gallbladder to contract, releasing bile produced by the liver into the small intestine.

Simple summary:

• Secretin → bicarbonate from the pancreas and increased bile production by the liver.

• CCK → digestive enzymes from the pancreas and bile release from the gallbladder.

What hormone stimulates secretion of pancreatic enzymes?

The hormone that stimulates secretion of pancreatic digestive enzymes is Cholecystokinin (CCK).

• CCK is released by the duodenum when fatty acids and proteins enter the small intestine.

• It stimulates the pancreas to release enzyme-rich pancreatic juice.

• It also causes the gallbladder to contract and release bile.

Quick answer: Cholecystokinin (CCK) stimulates secretion of pancreatic enzymes.

state how the mucosa of the small intestine differs from that of the stomach, and explain the functional significance of the differences

Small intestine mucosa vs. stomach mucosa:

• The small intestine mucosa has circular folds, villi, and microvilli, which greatly increase the surface area for absorption. It also contains cells specialized for absorbing nutrients.

• The stomach mucosa lacks villi and microvilli. Instead, it contains gastric pits and glands that secrete acid, enzymes, and mucus for digestion.

Functional significance:

• The stomach’s mucosa is specialized for secretion and the beginning of digestion.

• The small intestine’s mucosa is specialized for completing digestion and absorbing nutrients, thanks to its greatly increased surface area.

define contact digestion and describe where it occurs

Contact digestion is the final stage of chemical digestion in which digestive enzymes are attached to the microvilli (brush border) of the small intestine rather than being released into the intestinal lumen. As nutrients touch the brush border, these enzymes break them down into molecules small enough to be absorbed.

Where it occurs:

• On the brush border of the small intestine, especially in the duodenum and jejunum.

• Enzymes involved include maltase, sucrase, lactase, and peptidases.

Simple definition:
Contact digestion is digestion that occurs when food molecules come into direct contact with enzymes attached to the microvilli of the small intestine.

describe the types of movement that occur in the small intestine.

The small intestine has two main types of movement:

1. Segmentation

• ring-like contractions that mix chyme with digestive juices

• helps digestion and absorption

2. Peristalsis

• wave-like contractions that push chyme forward through the intestine

• moves contents toward the large intestine

state how the mucosa of the small intestine differs from that of the stomach, and explain the functional significance of the differences

Differences in the Mucosa

• The small intestine mucosa has villi and microvilli that increase surface area for absorption.

• The stomach mucosa does not have villi. Instead, it has gastric pits and glands that secrete acid and digestive enzymes.

Functional Significance

• The small intestine is specialized for nutrient absorption, so the villi and microvilli provide a large surface area.

• The stomach is specialized for digestion and secretion, so its mucosa is designed to produce acid, mucus, and enzymes rather than absorb nutrients.

 

describe the digestive secretions and functions of the liver

Liver

Digestive Secretion: Bile

Functions of bile:

• Emulsifies fats (breaks large fat globules into smaller droplets), making them easier for enzymes to digest.

• Helps absorb fats and fat-soluble vitamins (A, D, E, and K).

• Carries waste products such as bilirubin and excess cholesterol for elimination.