Human Anatomy: Abdomen

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Questions and Answers

What is the primary function of the portal vein?

Drains blood from the abdominal GI tract to the liver (correct)

Drains blood from the heart to the lungs

Transports lymphatic fluid to the bloodstream

Carries oxygen-rich blood from the liver to the body

Which muscle is primarily responsible for maintaining fecal continence?

Puborectalis (correct)

Iliococcygeus

Levator ani

Pubococcygeus

Which part of the uterus is responsible for the thick muscular wall?

Myometrium (correct)

Cervix

Endometrium

Fundus

Where does fertilization typically occur within the female reproductive system?

Infundibulum of the fallopian tube Signup and view all the answers

What is likely a consequence of injury during childbirth to the pelvic floor muscles?

Urinary stress incontinence Signup and view all the answers

Which of the following describes the position of the uterus when the bladder is full?

Retroverted and retroflexed Signup and view all the answers

What does the term 'ectopic pregnancy' refer to?

Implantation occurring outside the endometrial lining Signup and view all the answers

What is the primary function of the epididymis in the male reproductive system?

Maturation and storage of sperm Signup and view all the answers

What is the role of the greater vestibular glands?

Lubricating the vaginal opening Signup and view all the answers

What is a common result of cryptorchidism if left uncorrected?

Infertility and increased cancer risk Signup and view all the answers

What is the primary role of the seminal vesicles in male reproductive anatomy?

Contributes to the volume of semen Signup and view all the answers

Which zone of the prostate is most commonly affected by prostate cancer?

Peripheral zone Signup and view all the answers

What type of secretion do the bulbourethral glands produce?

Mucous for lubrication Signup and view all the answers

What is a common symptom of benign hypertrophy of the prostate?

Intermittent urinary stream Signup and view all the answers

Which muscle is primarily responsible for mediating erection in the penis?

Ischiocavernosus muscle Signup and view all the answers

Which structure in the kidney is responsible for urine secretion?

Renal pyramids Signup and view all the answers

What is the main function of the urinary bladder?

Stores urine Signup and view all the answers

How does the left renal vein differ from the right renal vein?

It crosses the midline before draining into the IVC Signup and view all the answers

What area does the urethra naturally traverse as it connects the bladder to the exterior?

Corpus spongiosum Signup and view all the answers

Where does the urine go after it is secreted from the renal pyramids?

Minor calyx Signup and view all the answers

What is the primary position of the azygos vein in relation to the vertebral column?

Posteriorly positioned against the vertebral column Signup and view all the answers

Which of the following structures does not drain into the azygos vein?

Heart Signup and view all the answers

What is the primary function of the conjoint tendon in relation to the internal and transverse abdominal muscles?

To create a fibrous compartment Signup and view all the answers

Which muscle is primarily responsible for filling the space between the 12th rib and the iliac crest in the posterior abdominal wall?

Quadratus Lumborum Signup and view all the answers

What type of hernia occurs due to increased abdominal pressure causing abdominal contents to protrude?

Inguinal hernia Signup and view all the answers

Which layer is the deepest in the anterior abdominal wall structure?

Transversalis fascia Signup and view all the answers

What is the primary component of the inguinal canal's posterior wall?

Transversalis fascia Signup and view all the answers

At what stage of development do the testes begin their descent into the scrotum?

About 7 months during gestation Signup and view all the answers

Which structure in the abdomen is lined by the visceral peritoneum?

Intraperitoneal viscus Signup and view all the answers

Which abdominal layer typically provides more stability and compartmentalization?

Rectus sheath Signup and view all the answers

What is the role of the mesentery in the abdomen?

Provides a pathway for nerves and vessels Signup and view all the answers

Which part of the small intestine is primarily responsible for most nutrient absorption?

Jejunum Signup and view all the answers

Which statement correctly describes the pyloric sphincter?

Controls the amount of chyme entering the duodenum Signup and view all the answers

What does the term 'retroperitoneal' refer to in abdominal organ positioning?

Organs situated behind the peritoneum Signup and view all the answers

Where does the duodenum primarily receive pancreatic enzymes and bile?

At the major duodenal papilla Signup and view all the answers

What anatomical feature does the spleen have that distinguishes it from other abdominal organs?

Being the largest lymphatic organ Signup and view all the answers

What is the main function of the gallbladder?

To store and concentrate bile Signup and view all the answers

What distinguishes the liver's visceral surface?

It is concave due to impressions of adjacent organs Signup and view all the answers

Which of the following is true regarding the abdominal aorta's branches?

The superior mesenteric artery supplies the midgut Signup and view all the answers

What is unique about the structure of the large intestine's outer longitudinal muscle layer?

It forms three distinct bands called tenia coli Signup and view all the answers

What type of blood does the azygos vein primarily drain?

Deoxygenated blood from thoracic organs Signup and view all the answers

Where does the azygos vein arch before draining into the superior vena cava?

Over the right lung root Signup and view all the answers

Which of the following is a function of the inguinal canal?

To transport the testes from the abdomen to the scrotum Signup and view all the answers

What type of abdominal wall muscle is the external oblique?

Superficial layer muscle Signup and view all the answers

What does the term 'retroperitoneal' describe?

Organs located behind the peritoneum Signup and view all the answers

What fibrous structure connects the testes to the scrotum during descent?

Gubernaculum Signup and view all the answers

How many main layers of muscle does the lateral flat muscle group in the anterior abdominal wall consist of?

Three layers Signup and view all the answers

Which muscle is primarily responsible for flexing the hip and is located in the posterior abdominal wall?

Psoas major Signup and view all the answers

What is the anatomical significance of the cervical constriction of the oesophagus?

It is the narrowest part of the oesophagus. Signup and view all the answers

Which structure forms the floor of the inguinal canal?

Inguinal ligament Signup and view all the answers

Which function is primarily associated with the mesentery?

Providing a pathway for nerves and vessels Signup and view all the answers

What anatomical structure supports the anterior abdominal wall and contains the rectus abdominus muscle?

Rectus sheath Signup and view all the answers

What defines the pyloric sphincter?

It is formed by the merging of circular muscle layers at the distal end of the pyloric canal. Signup and view all the answers

What is the primary role of the testicular gubernaculum during development?

To guide the testes descent Signup and view all the answers

Which part of the small intestine is primarily retroperitoneal?

Duodenum Signup and view all the answers

What is the primary purpose of the peritoneum in the abdomen?

Lining the abdominal cavity and organs Signup and view all the answers

Where does the transverse colon begin?

At the hepatic flexure Signup and view all the answers

What anatomical boundary defines the location of the right lower quadrant in the abdomen?

Median plane Signup and view all the answers

Which structure separates the liver into its two main lobes?

Falciform ligament Signup and view all the answers

Which muscle is not considered to support the anterior abdominal wall?

Pyramidalis Signup and view all the answers

What anatomical feature does the spleen have that enhances its functions?

A delicate capsule Signup and view all the answers

What is the role of the gallbladder?

To concentrate and store bile Signup and view all the answers

What distinguishes the jejunum from the ileum regarding its structure?

Jejunum has more mucosal folds. Signup and view all the answers

Which artery supplies blood to the midgut?

Superior mesenteric artery Signup and view all the answers

What is true about the large intestine's wall structure?

The outer layer is split into three bands called tenia coli. Signup and view all the answers

What is the function of the hepatic veins?

To drain venous blood from the liver to the inferior vena cava. Signup and view all the answers

What is the primary characteristic of the visceral surface of the liver?

It interfaces with other organs and is concaved. Signup and view all the answers

Study Notes

Portal Vein

Drains blood from the abdominal GI tract, spleen and pancreas
Carries venous blood to the liver for metabolism
Metabolised blood drains into the hepatic veins, which drain into the IVC

Pelvic Diaphragm

Separates pelvis and perineum
Attachment point for external genitalia
Diamond shaped with two triangles:
- Urogenital triangle
  - Anterior
  - Contains urogenital hiatus
- Anal triangle
  - Posterior
  - Contains anal aperture
Formed by levator ani muscle:
- Puborectalis
  - Attaches to the pubis bone and goes around the rectum
  - Forms a sling around the rectum
  - Contributes to faecal continence
- Pubococcygeus
  - Lateral to puborectalis
  - Attaches to the pubis and coccyx bones
- Iliococcygeus
  - Lateral to pubococcygeus
  - Attaches to the ilium and coccyx bones

Perineal Membrane

Covers half of the pelvic diaphragm (urogenital triangle)
Superficial to the pelvic diaphragm
Opening for the urethra (male and female) and vagina (female)

Deep Perineal Pouch

Space between perineal membrane and levator ani
Contains skeletal muscles that form voluntary sphincters around the urethra (external urethral sphincter) and the vagina

Child Birth

Perineum, levator ani, perineal membrane and deep perineal pouch muscles are often torn or injured
In females, these muscles support the urethra, vagina, uterus and rectum
Injury can result in urinary stress incontinence, uterine prolapse and faecal incontinence

Ovary

Paired
Intraperitoneal
Located posterior to the broad ligament and adjacent to the lateral wall of the pelvis
Ovarian artery supplies the organ
Ligament of ovary attaches the ovary to the uterus
Irregular shaped ball
Two regions:
- Inner medulla
  - Contains vessels, nerves and lymphatics
- Outer cortex
  - Follicular genesis occurs here
Defined surface epithelium
Oocytes are surrounded by supporting cells, which prepare the oocyte for ovulation
Oocyte ovulates into the fallopian tube

Fallopian/Uterine Tubes

Project laterally from the uterus and open adjacent to ovaries
Three areas:
- Infundibulum
  - Funnel shaped
  - Facilitates oocyte collection
  - Fimbriae attach to the anterior and lateral part of the ovary and help to catch the oocyte
- Ampulla
  - Large
  - Labyrinthine lumen
  - Fertilization occurs here
- Isthmus
  - Narrow
  - Connects to uterus

Uterus

Thick walled, muscular
Facilitates development of the embryo and foetus
Uterine artery supplies the organ
Three parts:
- Fundus
  - Top part, above fallopian tubes
- Body
  - Largest part, below fallopian tubes
- Cervix
  - Opening into the vagina
Two linings:
- Myometrium
  - Middle layer made of smooth muscle
  - Undergoes hypertrophy and hyperplasia during pregnancy
- Endometrium
  - Inner lining
  - Supports pregnancy
  - Sheds during menstruation
Position of the uterus (when the bladder is empty):
- Anteverted relative to the vagina
- Anteflexed over the bladder
When the bladder is full, uterus is displaced upwards
Retroverted and retroflexed uterus is displaced to the back and more likely to prolapse
Uterine prolapse is the uterus pushed through the vagina due to high pressure in the pelvis

Cervix

Opens inferiorly into the anterior wall of the vagina
Two parts:
- Supravaginal (above vagina)
- Vaginal (in vagina)
Uterus is best supported at the cervix

Vagina

Muscular passage
Connects uterus to the exterior
Between the urethra anteriorly and rectum posteriorly
Fornix is the space created anterior, posterior and lateral to where the cervix enters the vagina
Vaginal arteries supply the organ

Ectopic Pregnancy

Fertilization occurs in the ampulla
Implantation normally occurs in the uterine body
Ectopic/extrauterine pregnancy is implantation anywhere but the endometrial lining
The embryo will grow in areas with a large blood supply
Causes bleeding into the abdominal cavity
Burst uterine tube is often misdiagnosed as a burst appendix

Peritoneal Folds

Peritoneum covers the top visceral layer of the pelvis
Supports and protects the pelvis
Peritoneal folds form over the pelvic viscera
Broad ligament is peritoneal folds coming together over the uterine tube
Ovaries are surrounded by peritoneum and therefore are intraperitoneal
Ligament of ovary is folds of peritoneum over the ovarian vessels

Peritoneal Pouches

Created by peritoneal folds
Recto-uterine pouch
- Between the rectum and uterus
- Deepest part of the abdominal cavity
- Fluid collects here, especially if the patient lies on their back
- Fluid can be aspirated with a syringe through the fornix
Vesico-uterine pouch
- Between the bladder and uterus

Development of External Genitalia

Same in males and females
Genital tubercle develops into the glans penis (male) or glans clitoris (female)
Testosterone causes more rapid growth of the genital tubercle resulting in it being larger in males
Urethral folds develop into the urethra (male and female) and labia minora (female)
Labioscrotal swellings develop into the scrotum (male) and labia majora (female)

Anatomy

Vulva/pudendum is the erectile tissue and overlying skin which comprises the external genitalia
Labia minora are two thin skin folds beside the midline, fat free and hair free with connective tissue inside
Vestibule is the area between each labia minora (contains the urethra and vagina)
Labia majora are larger skin folds, lateral to labia minora
Glans clitoris is erectile tissue, exposed, located where the labia minora meet anteriorly
Perineal membrane and pubic arch are attachment points for the roots of external genitalia

Erectile Tissue

Erectile tissue is formed by:
- Two corpora cavernosa (anterior to glans clitoris, attaches to pubic arch)
- Two bulbs of vestibule (deep to labia minora)
- Glans clitoris
Body of clitoris contains corpora cavernosa and bulbs of vestibule
Erectile tissues are anterior to the urethra
Greater vestibular glands are posterior to bulbs, have openings into the vestibule, secrete lubricating mucous during arousal

Muscles

Ischiocavernosus muscle covers crus of clitoris and maintains erection of the clitoris
Bulbospongiusis muscle encloses the bulbs and greater vestibular glands, supports the pelvic floor, assists in clitoral erection and compresses greater vestibular glands

Pelvic Diaphragm (Male)

Same as female pelvic diaphragm
Only one opening in the perineal membrane for the urethra
Deep perineal pouch also has sphincters around glands

Perineal Membrane (Male)

Superficial to the pelvic diaghragm
Covers the urogenital triangle
Opening for the urethra (male & female) and vagina (female)

Deep Perineal Pouch (Male)

Space above the perineal membrane
Contains skeletal muscle that form sphincters around the urethra, glands, & neurovascular structures that supply the penis

Testes

Function in sperm production
Septa divides the testes into ~250 lobules
Lobules contain 3–10 seminiferous tubules
Each tubule is a highly convoluted loop in the lobule
The closer to the lumen, the more the sperm differentiate (still non-motile)
In the mediastinum, tubules end as tubulus erectus, which connects to the rete testis
Rete testis is an anastomosing channel system, collects sperm from all the seminiferous tubules
Outer capsules:
- Tunica albugenia surrounds lobules
- Tunica vaginalis covers testes during descent, extension of abdominal peritoneum, surrounds tunica albugenia

Testicular Decent

Gonadal development occurs along the posterior abdominal wall
Testes descend towards the inguinal canal by seven months of gestation
Through the inguinal canal into the scrotum just before birth
Drags blood vessels, nerves, duct system (vas deferens) and layers of abdominal wall to the scrotum

Cryptorchidism (undescended testes)

Histological changes à infertility
Increased risk of testicular cancer
Needs to be surgically corrected before 18 months

Epididymis

Coiled tube
~5 cm long
Sperm in the mediastinum of the testes travel through efferent tubules to the epididymis.
Three parts:
- Capus (head)
- Corpus (body)
- Caudal (tail)
Surrounded by smooth muscle to assist movement of sperm
Function to store and mature sperm
Where sperm acquire motility
Sperm are stored for ~1 month

Vas Deferens

Sperm travels from the epididymis to the vas deferens
Long duct
Length and complex course results from testicular descent
Penetrates abdominal wall through the inguinal canal
Descends along the lateral wall of the pelvic cavity
Wolffian ducts develop into the vas deferens
Smooth muscular duct
Muscular duct which transports spermazoa to ejaculatory duct
Ejaculation is mediated by the sympathetic nervous system
Ejaculatory duct is the vas deferens and duct of seminal vesicle
Function is to transport sperm to ejaculatory duct
Part of the spermatic cord

Vasectomy

Ligating the vas deferens to prevent sperm from reaching the penis
Vas is superficial at the posterior side of the scrotum
White blood cells assist the epididymis to break down sperm after a vasectomy

Accessory Glands

Contribute to the volume of ejaculate

Male Reproductive System

Seminal vesicles
- Posterior surface of bladder
- Ducts of seminal vesicle combine with vas deferens to form ejaculatory duct
- Contribute to volume of semen
- Secrete alkaline fluid
- Help with sperm motility and viability
Prostate
- Inferior to bladder, anterior to rectum
- Size of a walnut
- Secretes watery liquid with zinc, citric acid, and proteolytic enzymes
- Assists with sperm viability and maturation
- Benign hypertrophy of prostate:
  - Occurs in most elderly men
  - Hypertrophy of central prostate
  - Compresses/blocks urethra causing intermittent urinary stream
- Prostate cancer:
  - Common malignancy in men
  - Effects the entire prostate
  - Treated with radiotherapy, surgery, or androgen deprivation therapy
Bulbourethral glands
- Pea-shaped, paired
- Located in the deep perineal pouch
- Ducts open into the spongy urethra
- Produce mucous secretion that lubricates urethra
External genitalia
- Ejaculatory tissues covered by skin
- Scrotum:
  - Homologue of labia majora
  - Skin fuses in the midline
- Penis
  - Covered by skin
  - Composed of:
    - 2 corpora cavernosa
    - 1 corpus spongiosum (expands distally to form glans penis)
  - Erection: mediated by parasympathetic nervous system

Kidneys and Urinary System

Kidneys
- Function to produce urine
- Retroperitoneal, bean shaped
- Extend longitudinally from T12-L3
- Renal capsule lines kidney surface
- Renal sinuses are spaces within the kidney, filled with perinephric fat
- Inner medulla:
  - Contains renal pyramids
  - Secretory cells secrete urine
- Outer cortex:
  - Continuous layer surrounding medulla
- Renal collecting system:
  - Urine secreted from the medulla into the hilum
  - Urine is collected into the minor calyx, then the major calyx, then the renal pelvis
- Renal hilum:
  - Faces anteromedially
  - Holds the renal vein, renal artery, and renal pelvis
  - Renal artery:
    - Supplies blood to each kidney
    - Divides into 5 segmental arteries within the hilum
  - Accessory renal artery:
    - Additional blood supply
    - Can enter the kidney via the hilum or the surface
  - Renal vein:
    - Drains venous blood of the kidneys
    - Left renal vein crosses midline and is longer than the right renal vein
Ureters
- Paired hollow viscus
- Extend from the kidneys into the pelvis
- Constrictions:
  - Uretropelvic Junction
  - Where ureter crosses the pelvic brim
  - Where ureter enters the bladder
Urinary bladder
- Hollow viscus
- Strong muscular walls
- Function to store urine
- Apex anteriorly, against pubis bone
- Base posteriorly, against uterus in females or rectum in males
- Bladder neck:
  - Inferiormost part
  - Anchors the bladder
  - As the bladder fills, the top expands and is free but the neck stays put
- Base:
  - Forms an inverted triangle (trigone)
  - Contains 2 uretric orifices and 1 urethral orifice
Urethra:
- Passes urine from the bladder to the exterior

Azygos Vein

Drains venous blood from the thorax into the superior vena cava (SVC)
Drains both the parietal and visceral compartments of the thorax, excluding the heart
Drains venous blood from organs supplied by the descending aorta including the thoracic walls, pericardium, lungs, trachea, bronchi, esophagus, and diaphragm
The position of the azygos vein against the vertebral column, and the heart's more anterior position, force the azygos vein to arch anteriorly over the right lung root before draining into the SVC.
An impression of the azygos vein can be seen on the medial surface of the right lung.

GI Tract

The abdomen is the cavity located between the thorax (above) and pelvis (below).
The abdominal wall is primarily composed of muscle and associated structures, not bone.

Anterior Abdominal Wall

Bony Framework

The bony framework consists of the bones of the thorax (superiorly) and pelvis (inferiorly).
The anterior abdominal wall structures attach to:
- Inferior border of the thorax
- Iliac crest
- Anterior superior iliac spine (ASIS)
- Pubic tubercle
- Pubic crest

Covering Structures

8 layers, listed from superficial to deep:
- Skin
- Superficial fascia
- 3 paired muscles (External Oblique, Internal Oblique, Transversus Abdominus)
- 2 vertical muscles (Rectus Abdominus, Pyramidalis)
- Transversalis fascia
- Extra-peritoneal fascia
- Peritoneum

Lateral Flat Muscles (3 Paired, 3 layers)

3 paired layers, fleshy laterally, replaced with aponeuroses medially.
Aponeuroses allow the abdomen to expand and create the linea alba.
Aponeuroses from both sides interdigitate to form the linea alba, a raphe (seam) that runs along the midline.

External Oblique (EO) Muscles

Superficial layer
Fibre direction: inferomedial
Medial attachment: linea alba
Superior attachment: ribs (EO fibres overlap the costal margin)
Posterior attachment: thoracolumbar fascia with the posterior abdominal wall
Inferior attachment:
- Lateral part: iliac crest and ASIS
- Central part: free
- Medial part: pubic tubercle and pubic crest
Inguinal Ligament:
- Formed by the free, central part of the inferior border of the EO.
- Thickened as it curves under and extends from ASIS to the pubic tubercle.

Internal Oblique (IO) Muscles

Intermediate layer
Fibre direction: superomedial (perpendicular to EO)
Medial attachment: linea alba
Superior attachment: costal margin
Posterior attachment: thoracolumbar fascia
Inferior attachment: lowermost IO fibres arise from the lateral 2/3 of the inguinal ligament, arch up, then go down to insert on the pubic crest via a conjoint tendon.

Transversus Abdominus (TA) Muscles

Deep layer
Fibre direction: transverse
Medial attachment: linea alba
Superior attachment: costal margin
Posterior attachment: thoracolumbar fascia
Inferior attachment: lowermost TA fibres arise from the lateral 1/3 of the inguinal ligament, arch up, then go down to insert on the pubic crest via a conjoint tendon.
Conjoint Tendon: a common tendon where the IO and TA muscles insert.
Transversalis fascia is deep to the TA muscles.

Medial Vertical Muscles

Rectus Abdominus

Located on either side of the linea alba
Primary vertical muscle supporting the anterior abdominal wall
Origin: pubis
Insertion: ribcage (overlaps costal margin)
3 tendinous intersections strengthen the muscle (4 short muscles, not 1 long)
Rectus Sheath:
- Created by the aponeuroses of the EO, IO, and TA, which pass in front or behind the rectus abdominus.
- Creates a fibrous compartment for the rectus abdominus.
- EO aponeurosis: in front
- IO aponeurosis: splits, passes in front and behind
- TA aponeurosis: behind

Pyramidalis Muscles

Pyramid-shaped, small, and do not support the anterior abdominal wall.

Testicular Descent

Testes develop high in the posterior abdominal wall, within extra-peritoneal fat.
Descent into the scrotum is necessary for spermatogenesis as normal core body temperatures inhibit sperm production.
A 2-3°C lower temperature is ideal for spermatogenesis.
Testes connect to the scrotum through the gubernaculum, a fibrous cord present in both males and females.
Testicular descent occurs around 7 months during gestation.

Inguinal Rings

To leave the abdomen from extra-peritoneal fat, a hole in the transversalis fascia and EO aponeurosis must be created.
Deep Inguinal Ring: circular hole in the transversalis fascia.
Superficial Inguinal Ring: triangular split in the EO aponeurosis (fibrous split at inferior attachment).
The path between the deep and superficial inguinal rings is oblique.

Inguinal Canal

The path the testes take during descent into the scrotum.
It transverses the transversalis fascia (deep inguinal ring), TA, IO, and EO (superficial inguinal ring) layers.
The inguinal canal is superior to the inguinal ligament, and its boundaries are:
- Floor: inguinal ligament
- Roof: arching IO and TA fibres
- Anterior wall: EO aponeurosis and IO fibres (laterally)
- Posterior wall: transversalis fascia and conjoint tendon (medially)
Upon emerging from the superficial inguinal ring, it becomes the spermatic cord.
Women also have inguinal canals, although they are less prominent.

Inguinal Hernia

The inguinal canal is a communicating structure between the abdomen and the perineum.
Increased abdominal pressure can lead to abdominal contents protruding through the abdominal wall at weak spots, resulting in a hernia.
Inguinal hernia: protrusion of abdominal contents into the inguinal canal.

Cryptorchidism

Undescended testes
Can be located in the abdomen, inguinal canal, or pre-scrotal region.
Requires surgical correction before 18 months to 2 years of age.
Can cause infertility and increases the risk of testicular cancer.

Posterior Abdominal Wall

Consists of muscle and lumbar vertebrae.
Attaches to the bony thorax, pelvis, and vertebrae.
- Superiorly: 12th rib
- Medially: lumbar vertebrae
- Laterally: thoracolumbar fascia
- Inferiorly: iliac crest

Psoas Major

Paired muscle (on either side of the lumbar vertebrae).
Longitudinally oriented.
Arises from the lumbar vertebrae bodies.
Passes inferiorly and under the inguinal ligament.
Inserts on the lesser trochanter of the femur.
Psoas Minor: - Lines the surface of the psoas major anteriorly. - Smaller than the psoas major. - Not present in all people, or on both sides.

Quadratus Lumborum

Lateral to psoas major.
Paired muscle on either side of psoas major
Arises from the 12th rib and the tips of the lumbar vertebrae transverse processes.
Inserts onto the iliac crest.
Fills the space between the 12th rib and the iliac crest.

Iliacus

Paired muscle
Fills the space in the iliacus fossa of the hipbone.
Situated inferior to the quadratus lumborum and lateral to the psoas major.

Thoracolumbar Fascia

Muscles of the anterior and posterior abdominal walls, and back muscles are enclosed within the thoracolumbar fascia.
The fascia of the anterior and posterior abdominal walls meet lateral to the quadratus lumborum.
The posterior abdominal wall muscles end where the anterior abdominal wall muscles begin.
It creates a complete muscular wall.

Abdominal Quadrants

Median Plane: vertically oriented from the xiphoid process to the pubic symphysis.
Transumbilical Plane: horizontally oriented and crosses the umbilicus.
Creates 4 quadrants: left upper, right upper, left lower, right lower.
Used to describe the positioning of abdominal viscera.

Peritoneum

The innermost layer of the abdominal walls.
Parietal peritoneum: lines the abdominal wall.
Visceral peritoneum: lines the viscera.
Peritoneal cavity: potential space between parietal and visceral peritoneum.
Intraperitoneal viscus: suspended within the abdominal cavity, completely lined with visceral peritoneum.
Retroperitoneal viscus:
- Sits against the posterior abdominal wall.
- Outside the abdominal cavity.
- Inner surface lined with parietal peritoneum.
- Example: kidneys.### Mesentery
A double fold of peritoneum that contains nerves, vessels and provides motility.
Not all viscera in the abdomen have a mesentery.
Intraperitoneal viscera have mesentery, retroperitoneal viscera do not.

Oesophagus

Begins at C6, descends down the midline and passes through the diaphragm at T10.
Enters the stomach from the right side.
Muscular tube with inner circular and outer longitudinal muscles.

Oesophageal Constrictions

Cervical constriction: anatomical sphincter at C6 where the oesophagus begins
Thoracic constriction: at T4/5, where the oesophagus is compressed from the left side by the bifurcation of the trachea and aortic arch
Diaphragmatic constriction: occurs at T10, where the oesophagus passes through the diaphragm, creating a functional sphincter.

Oesophagogastric Junction

Where oesophageal mucosa changes to stomach mucosa.
Sudden change, indicated by the Z-line.

Stomach

Located in the left upper quadrant, it's a dilated, hollow, J-Shaped viscus.
Intraperitoneal, with two openings:
- Cardiac Orifice: proximal, where oesophagus enters the stomach.
- Pyloric Orifice: distal, where the duodenum starts.
Two curvatures:
- Lesser Curvature: right side.
- Greater Curvature: left side.
Two surfaces:
- Anterior Surface
- Posterior Surface
Four parts:
- Cardia: region near cardiac orifice.
- Fundus: part above cardiac orifice, holding gas.
- Body: majority of the stomach.
- Pyloric Part: distal narrowing.
  - Pyloric Antrum (wider)
  - Pyloric Canal (narrower, more distal)
Pyloric sphincter/Pylorus: anatomical sphincter at the end of the pyloric canal, controlling chyme entry into the duodenum and aiding absorption.
Rugae: gastric folds/mucosa on the internal surface.

Small Intestine

Hollow viscus, divided into three parts:
- Duodenum
- Jejunum
- Ileum
Function in digestion and absorption.
Two muscle coats:
- Inner Circular Muscles
- Outer Longitudinal muscles

Duodenum

Short, retroperitoneal, C-shaped section.
Located with the right kidney lateral and the head of the pancreas medial to it.
Four parts:
- 1st part (duodenal cap): immediately after the pylorus.
- 2nd part: descending component, between the right kidney and pancreas.
  - Papilla on internal medial wall: secretes pancreatic enzymes and bile into the duodenum.
  - Major duodenal papilla: secretes products from the bile duct and main pancreatic duct.
  - Minor duodenal papilla: superior to the major, secretes products from the accessory pancreatic duct.
- 3rd part: horizontal, crosses the midline.
- 4th part: hooks around and joins with the jejunum.

Jejunum

Large, proximal 40% of small intestine.
Intraperitoneal.
Resides in the left upper quadrant.
Larger caliber, holding more gastric contents due to the majority of absorption occurring here.
Mucosal folds increase surface area.
Thick-walled.
Highly vascularized with less fat in the mesentery (vessels and nerves are more visible).

Ileum

Large, distal 60% of the small intestine.
Intraperitoneal.
Resides in the right lower quadrant (changes during pregnancy).
Lower caliber, holding less gastric contents due to less absorption occurring here.
Fewer mucosal folds.
Less vascularized with less fat in the mesentery (vessels and nerves are less visible).

Large Intestine

Begins at the ileocecal junction where the ileum enters the large intestine.
Ascending colon: retroperitoneal, large intestine starts to ascend.
Transverse colon: intraperitoneal, begins at the hepatic/right colic flexure, traverses the midline, and is the longest part.
Descending colon: retroperitoneal, begins at the splenic flexure/left colic flexure near the spleen, descends, and becomes the sigmoid colon.
Sigmoid colon: intraperitoneal, bends inferiorly and medially (S-shaped), and becomes the rectum and anal canal.

Large Intestine Wall

Inner Circular Muscle: complete layer.
Outer Longitudinal Muscle: split into three bands (tenia coli), which create a baggy appearance due to the incomplete muscle layer (haustra).
Omental appendices: fatty tags along the tenia coli.

Caecum

Intraperitoneal.
Blind pouch.
Inferior to the ileocecal junction.
Located in the right lower quadrant.

Appendix

Intraperitoneal.
Located in the right lower quadrant, inferior to the ileocecal junction.
Base of the appendix is located where the three tenia coli bands meet.
Position varies, but the base remains constant.

Rectum

Retroperitoneal.
Tenia coli bands merge to form a complete outer longitudinal muscle layer.
No tenia coli, haustra, or omental appendices.

Liver

Located in the right upper quadrant.
Situated under the right dome of the diaphragm.
Solid viscus.
Partially protected by the thoracic cage.
Intraperitoneal.
Function in bile production and nutrient metabolism.

Diaphragmatic Surface

Anterior and superior.
Where the liver sits against the diaphragm.
Smooth.
Partially protected by the ribcage.
Covered by peritoneum.

Visceral Surface

Posterior and inferior.
Interface between the liver and other viscera.
Concaved due to impressions from adjacent structures.
Contains the inferior vena cava (IVC) and gallbladder.
Covered by peritoneum, except for the IVC and gallbladder.

Portal Hepatis

Hilum, holds vessels, nerves, lymphatics, and ducts.
Portal Triad:
- Portal Vein: carries venous blood from the GI tract, containing nutrients for metabolism in the liver.
- Hepatic Artery: principle arterial supply to the liver.
- Bile Duct: carries bile from the liver to the duodenum.

Hepatic Veins

Drain the venous blood from the liver.
Not located in the hilum.
Run through grooves.
Drain directly into the IVC.

Liver Lobes

Diaphragmatic Surface: falciform ligament separates the liver into two anatomical lobes (larger right and smaller left lobes).
Visceral Surface:
- Right and Left Anatomical Lobes: fissures and grooves contain structures.
  - Left Sagittal Fissure: ligaments run through.
  - Right Sagittal Fissure: IVC and gallbladder are located here.
- Between these fissures is the hilum, separating the liver into two more accessory lobes:
  - Caudate Lobe: above the hilum.
  - Quadrate Lobe: below the hilum.
- Accessory lobes are actually part of the right lobe.

Gallbladder

Located on the visceral surface of the liver.
Not covered in peritoneum.
Hollow viscus.
Resides in the right upper quadrant.
Four parts:
- Fundus: blind end.
- Body:
- Neck: narrowing.
- Cystic Duct:
Stores and concentrates bile produced by the liver.
Overconcentration of bile can lead to gallstones.

Bile Pathway

Bile travels from the liver through the hepatic ducts to the common hepatic duct.
The common hepatic duct merges with the cystic duct to form the common bile duct.
The common bile duct enters the duodenum through the major duodenal papilla.
The major duodenal papilla has a functional sphincter.
Contraction of the sphincter (regulated by nerves) closes the sphincter, causing bile to fill and collect in the gallbladder.
Contraction of the gallbladder pushes bile through the cystic and bile ducts into the duodenum.

Pancreas

Resides in the left upper quadrant.
Retroperitoneal.
Solid viscus.
Four parts:
- Head: surrounded by the C-shaped duodenum.
- Neck:
- Body:
- Tail: located against the spleen.
Exocrine and endocrine functions.

Pancreatic Secretions

Exocrine secretion into the duodenum:
- Main pancreatic duct: collects pancreatic enzymes from the tail, body, neck, and head, and secretes them into the duodenum via the major duodenal papilla.
- Accessory pancreatic duct: collects pancreatic enzymes from the head, and secretes them into the duodenum via the minor duodenal papilla.

Spleen

Resides in the left upper quadrant.
Solid viscus.
Intraperitoneal.
Associated with GI tract organs.
Largest lymphatic organ.
Rich blood supply.
Two surfaces:
- Diaphragmatic Surface
- Visceral Surface: contains the hilum where the splenic arteries/veins enter/exit.
Located against the diaphragm and ribs 9, 10, and 11 on the left side.
Fracture of these ribs can cause damage to the spleen.
Soft and highly vascularized with a delicate capsule.
Sharp edges of fractured ribs can lacerate the capsule causing bleeding into the abdominal cavity.

Abdominal Aorta

Supplies abdominal organs.
Enters the abdomen at T12.
Bifurcates into the iliac arteries at L4.

Anterior Surface

Three Unpaired Branches:
- Supply unpaired viscera (GI tube).
- Celiac Trunk: foregut (abdominal esophagus to the major duodenal papilla).
- Superior Mesenteric Artery: midgut (major duodenal papilla to the distal 1/3 of the transverse colon).
- Inferior Mesenteric Artery: hindgut (distal 1/3 of the transverse colon to ½ way through the anal canal).
Three Paired Branches:
- Supply paired viscera.
- Suprarenal Arteries: adrenal glands.
- Renal Arteries: kidneys.
- Testicular/Ovarian Arteries: gonads.

Posterior Surface

Paired arteries supply abdominal wall structures.
Phrenic Arteries: diaphragm.
Parietal Arteries: anterior and posterior abdominal walls.

Venous Drainage

All abdominal venous blood drains into the IVC.
Venous blood from paired viscera and abdominal walls drains directly into the IVC.
Venous blood from unpaired viscera (except the liver) drains into the IVC via the portal vein.

Azygos Vein

Drains venous blood from the thorax into the superior vena cava (SVC)
Drains both parietal and visceral components of the thorax, excluding the heart
Receives venous blood from structures supplied by the descending aorta: thoracic walls, pericardium, lungs, trachea, bronchi, esophagus, and diaphragm
Its drainage pattern varies significantly among individuals
Located posteriorly against the vertebral column
Arches anteriorly over the right lung root to drain into the SVC
Creates an impression on the medial surface of the right lung

Abdominal Cavity

Located between the thorax (superior) and pelvis (inferior)
Abdominal wall primarily composed of muscle and coverings, not bone
Structures attach to the thorax and pelvis