Histology: Tissue Structures and Analysis

• Histology is the study of tissue structure and organization, involving fixed, sectioned, and stained samples

Four Tissue Types

• Connective tissue functions to cushion, support, and connect different body parts
  • Examples include areolar tissue, adipose tissue, tendon, and bone
• Muscle tissue facilitates movement through contraction
  • Skeletal, cardiac, and smooth muscles are examples
• Neural tissue transmits electrical impulses for communication
  • Neurons are the primary example
• Epithelial tissue covers body surfaces and lines cavities and involved in: Surface, Gland and Regeneration
  • Simple (squamous, cuboidal, columnar) and stratified (squamous, cuboidal, columnar) are examples

Thoracic Wall Spatial Relationships

• The thoracic wall includes bones, muscles, vessels, and nerves
• Superior thoracic aperture is the top opening of the thorax
• The thorax contains right and left pleural cavities and superior and inferior mediastinum
• The diaphragm separates the thoracic and abdominal cavities
• There are 12 ribs, with the 11th and 12th being floating ribs
  • Ribs attach to the sternum via costal cartilage
• 12 thoracic vertebrae make up the vertebral column in the thorax
• Ribs articulate with vertebrae in two places
  • The head of the rib articulates with the body of the vertebra
  • The tubercle of the rib articulates with the transverse process of the vertebra
• Intercostal bundles in the subcostal groove contain a vein, artery, and nerve (VAN)
• The right brachiocephalic vein, left brachiocephalic vein, superior vena cava, inferior vena cava, and azygous vein are major veins in the thorax
• Arterial supply includes the aorta, brachiocephalic trunk, right and left common carotid arteries, right and left subclavian arteries, and anterior and posterior intercostal arteries
• Arterial anastomosis provides alternate routes for blood flow if vessels are damaged
• The trachea divides into primary bronchi, which further divide into lobar bronchi, segmental bronchioles, and alveoli (for gas exchange)

Breast and Lymphatic Drainage

• Mammary glands contain lobes that produce milk
• Milk travels through lactiferous ducts to the nipple
• Lymphatic drainage to the axillary lymph nodes is important for breast cancer detection

Left vs. Right Lung

• The hilum is the medial surface of the lung where structures enter and exit
• The right lung has 3 lobes and is more prone to objects getting stuck (vertical orientation)
• The left lung has 2 lobes due to the presence of the heart

Visceral vs. Parietal Pleura

• Parietal pleura lines the walls of the thorax
• Visceral pleura covers the organs (lungs)
• Continuous structures with serous fluid in between to prevent friction and damage

Musculoskeletal Movements: Inspiration vs. Expiration

• Inspiration:
  • Elevation of ribs via external intercostals
  • Diaphragm contracts
  • Lungs expand
• Expiration:
  • Depression of ribs via internal and innermost intercostals and transversus thoracis
  • Diaphragm expands (phrenic nerve innervation, originates in the neck)
  • Lungs contract

Structures in Mediastinum and Heart

• The mediastinum is the area between the lungs
• The right heart collects deoxygenated blood from the body and pumps it to the lungs, contains the tricuspid and pulmonary semilumar
• The left heart collects oxygenated blood from lungs, returning to the body through lungs and contains the bicuspid (mitral) & aortic semilunar
• The vagus nerve wraps under the aorta, and the recurrent laryngeal nerve is a branch
• Papillary muscles and chordae tendineae prevent valves from opening backwards
• Blood from the coronary sinus drains to the right atrium

Layers of the Pericardium

• Fibrous pericardium is the thick outer layer
• Parietal serous pericardium adheres to the inside of the fibrous pericardium
• Visceral serous pericardium adheres directly to the heart

Anatomical Basis for Cardiac Defects

• Myocardial infarction is a blockage in a coronary artery, causing the heart to become ischemic
• Mitral valve prolapse occurs when the mitral valve does is not properly close, causing blood to leak back to the atrium
• Pericardial effusion is excess fluid in the pericardial sac

Developmental Heart Defects

• Patent foramen ovale: the foramen ovale doesn't close between the atria
• Patent ductus arteriosus: the ductus arteriosus doesn't degenerate between the pulmonary trunk and aorta
• Ventricular septal defect: the interventricular septum does not fully develop

Spinal Nerve Structure

• A nerve is a bundle of nerve cells (neurons) wrapped in connective tissue
• A synapse is an electrochemical connection between nerve cells and targets
• A ganglion is a thickened portion of a nerve, containing cell bodies
• A plexus is any mixture of nerve fibers

Divisions of the Nervous System

• CNS: brain, spinal cord containing white matter (myelinated) and grey matter (unmyelinated)
• PNS: spinal nerves, cranial nerves

Sensory vs Motor

• Sensory neurons:
  • Pseudo-unipolar
  • Dorsal root
  • Cell bodies outside CNS in the dorsal root ganglion
• Motor neurons:
  • Multipolar
  • Ventral root
  • Cell bodies inside CNS (lateral and ventral horns)

Somatic vs. Autonomic

• Somatic:
  • Voluntary
  • One-neuron pathway
  • Cell bodies in the ventral horn
• Autonomic:
  • Involuntary
  • Synapse before reaching target (ganglia)
  • Two-neuron chain
  • Cell bodies in the lateral horn

Sympathetic Trunk Structure

• Sensory cell bodies are located in the dorsal root ganglion
• Has dorsal and ventral roots connected to the spinal nerve

Parasympathetic vs Sympathetic Nervous System

• Parasympathetic:
  • Rest and digest
  • Cranial and sacral spinal nerves
  • Synapse at target
• Sympathetic:
  • Fight or flight
  • Thoracic and lumbar spinal nerves
  • Synapse in sympathetic trunk

Abdominal Wall

• Includes the rectus abdominis, external oblique, internal oblique, and transversus abdominis muscles
• Three openings in the diaphragm for: IVC, esophagus, aorta

Inguinal Canal and Spermatic Cord

• The inguinal canal provides a passage from the abdomen to the scrotum (male) or labia majora (female)
• Contains the spermatic cord
• Transversalis fascia becomes the internal spermatic fascia
• internal oblique becomes Cremaster muscle
• External oblique aponeurosis becomes the external spermatic fascia
• Round ligament also passes through the inguinal canal

Peritoneum Mesenteries

• The peritoneum lines the abdominal cavity
• The mesentery is a double-layer of peritoneum that suspends an intraperitoneal organ
• The greater omentum is a peritoneum that connect stomach and transverse colon
• The lesser omentum is a peritoneum connecting the stomach and duodenum

Peritoneal Organs

• Intraperitoneal organs are surrounded and suspended by a double fold of peritoneum
  • Examples include the spleen, liver, gallbladder, stomach, jejunum, ileum, transverse colon, and sigmoid colon
• Retroperitoneal organs lie directly against the body wall, only partly covered by the peritoneum
  • Primary retroperitoneal organs include the kidneys, suprarenal glands, aorta, and IVC
  • Secondary retroperitoneal organs include the duodenum, pancreas, ascending colon, and descending colon
• Zygote splitting without growing

Embryogenesis

• Morula multiple cells in zona pellucida (32+)
• Cells differentiate into two separate populations of cells in one zona pellucida
• Blastulation contains a blastocoel and outer ring of trophoblasts
• Epiblasts and hypoblasts make up the Amniotic cavity
• Where cells epiblast migrate through primitive streak in bilaminar disks makes up the trilaminar disks which are germ layers

Germ Layers

• Ectoderm (epiblast) develops into nervous system, epidermis, special sensory epithelia
• Mesoderm develops into bone, cartilage, connective tissue, muscle, heart, reproductive, serous membrane
• Endoderm (hypoblasts) develops into digestive and respiratory tracts epithelium, bladder and urethra, liver and pancreas

Abdominal Organs

• Pancreatic duct and common bile duct
• Acini secrete pancreatic juice (dark)
• Islets of Langerhans produce hormone that regulate blood glucose levels

Jejunum vs. Ileum

• Jejunum:
  • Thick wall
  • Closely packed plicae circulares
  • Long vasa recta
• Ileum:
  • Thinner wall
  • Widely spread plicae circulares
  • Short vasa recta arteries

Divisions of GI Tract

Divisions are foregut, midgut, and hindgut

• Foregut:
  • Stomach
• Liver
• Pancreas
• ½ duodenum
• Midgut:
• ½ duodenum
• Jejunum
• Ileum
• Colon (to ⅔ of transverse)
• Hindgut:
  • Rest of colon
  • Rectum

Blood Supply

• Celiac artery supplies the foregut
• Superior mesenteric artery supplies the midgut
• Inferior mesenteric artery supplies the hindgut

Innervation

• Parasympathetic innervation: Vagus for foregut and midgut, sacral nerves for hindgut
• Sympathetic innervation: splanchnic nerves
• Sensory innervation: Abdominal wall (somatic sharpness), abdominal organs (autonomic aching)

Histology of the GI Tract

• Stomach: simple columnar epithelium (gastric pits and glands)
• Small intestine: simple columnar covered by villi
• Colon: simple columnar, no villi (crypts)

Portal vs. Caval Venous System

• Blood from GI tract organs is filtered through the liver before entering IVC
• Venous blood drains directly into IVC via the caval system

Pelvic Wall And Floor Structure

• Perineal membrane: a layer of fascia attached to the pubic arch and ischia
• Perineum: below the pelvic diaphragm (levator ani)
• Pelvic floor muscles: levator ani and coccygeus
  • If the pelvic diaphragm is stretched and weakened, this can lead to urinary and fecal incontinence
  • Piriformis and obturator internus exit via greater and lesser foramina, causing hip rotation
  • The iliopsoas muscle causes hip flexion
• Anterior urogenital triangle and posterior anal triangle

Positioning and Overall Features

• All pelvic organs are subperitoneal
• Internal anal sphincter is smooth muscle
• The external anal sphincter is skeletal muscle
• the prostate gland is a junction between urinary and reproductive systems
• tunica albuginea is a protective covering that separates it

Spermatic chord Characteristics

• spermatic cord includes the ductus deferens, testicular artery, and testicular chord
• Spermatic chord blockage in the ejaculatory duct, preventing you from finding sperm and fluid from the seminal vesicle
• Contains 3 erectile bodies (2 corpus cavernosa, 1 corpus spongiosum)
  • Ischiocavernosus and bulbospongiosus muscles cover erectile bodies
  • Bulbospongiosus attaches to perineal bodies
• Vestibule leads a central space containing labia minora, urethral opening, vaginal opening

Path of Sperm

• Tunica albuginea --> Epididymis --> Vas deferens --> Ejaculatory duct --> Prostatic urethra --> Membranous urethra --> Spongy urethra

Path of the egg

• Ovary --> Fimbriae --> Fallopian tube --> Uterus --> Cervix --> Vaginal canal

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