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How much space is there for organs in the abdomen?

Very little; spleen, two kidneys, and two adrenal glands together weigh less than 1 lb

Into how many groups are digestive organs organized?

Two groups

What organs make up the gastrointestinal (GI) tract?

Oral cavity → pharynx → esophagus → stomach → small intestine → large intestine → anus

What are other names for the GI tract?

Digestive tract, alimentary canal, gut

What are the accessory digestive organs?

Salivary glands, teeth, tongue, liver, gallbladder, pancreas

Are accessory digestive organs part of the gut tube itself?

No, they are mostly external but connected by ducts

Where are the big and minor deviations from the gut’s common blueprint?

Big: oral cavity, Minor: esophagus

What is the “common blueprint” of the gut wall?

A long cylindrical tube with a central lumen and four concentric layers

What are the four layers of the gut wall from inside to outside?

Mucosa → Submucosa → Muscularis externa → Serosa

What is the mucosa?

A membrane lining a body cavity open to the outside (oral cavity and anus)

What lines the luminal surface of the mucosa?

Epithelium

Why is the mucosal surface always wet?

Because of mucus

Does mucus composition differ in the gut?

Yes, for example, mouth and anus mucus are different

What is the lamina propria?

Loose connective tissue beneath the epithelium containing lymphatic vessels, nerves, small glands, and lymphoid tissue

What is GALT?

Gut-associated lymphoid tissue in the lamina propria

What is MALT?

Mucosa-associated lymphoid tissue

What is the muscularis mucosae?

Layer of smooth muscle covering the lamina propria

How are the layers of the muscularis mucosae arranged?

Inner circular layer near the lumen, outer longitudinal layer parallel to gut axis

What is the function of the muscularis mucosae?

Change contour of mucosal surface to increase absorption efficiency

What is the submucosa composed of?

Dense connective tissue

What is the function of the submucosa?

Distribution center for vessels and nerves, penetrated by branches to other gut layers

What types of vessels and nerves pass through the submucosa?

Lymphatic vessels, arteries, veins, sensory fibers, autonomic fibers (sympathetic and parasympathetic)

What is the function of sensory fibers in the submucosa?

Sense stretch of the gut wall and detect pain if overstretched

What is a submucosal plexus (Meissner’s plexus)?

A collection of parasympathetic neuron cell bodies that control the muscularis mucosa

What glands are found in the submucosa of the small intestine?

Brunner’s glands in the duodenum

Where is lymphoid tissue (GALT) specifically found in the gut?

In areas such as Peyer’s patches

What layers make up the muscularis externa?

Inner circular layer and outer longitudinal layer of smooth muscle

What nerve fibers are present in the muscularis externa?

Sensory/afferent fibers and autonomic parasympathetic and sympathetic fibers

What is the myenteric (Auerbach’s) plexus?

Cell bodies of parasympathetic neurons in the muscularis externa that control peristalsis

What is the serosa?

Thin layer of simple squamous epithelium (mesothelium) plus connective tissue covering organs in the abdominal cavity

What does the serosa secrete?

Watery, slippery fluid to lubricate organs and reduce friction

Why is the oral cavity different from the gut blueprint?

Because its mucosa classification depends on exposure and function, not just layers

What are the three types of oral mucosa based on function?

Masticatory, Non-masticatory (lining), Specialized

Where is masticatory mucosa found?

Gingiva (gums) and hard palate

What are the three patterns of masticatory mucosa?

1) Gums and raphe, 2) Fatty zone, 3) Glandular zone

What layers are missing in the “incomplete mucosa” of masticatory areas?

Muscularis mucosa, submucosa, muscularis externa, serosa

What are the three types of stratified squamous epithelium in the oral cavity?

Keratinized, Non-keratinized, Para-keratinized

What is unique about non-keratinized epithelium?

No keratin, no stratum granulosum, lucidum, or corneum; has stratum superficiale

Where is non-keratinized epithelium located?

Limited areas of gingiva, cheeks, ventral tongue, floor of mouth, soft palate

What is para-keratinized epithelium?

Similar to keratinized, but the corneum layer is nucleated

Where is specialized mucosa found?

Dorsal surface of the tongue

What areas does specialized mucosa of the tongue include?

1) Root (back), 2) Taste bud area (front)

What separates the root and specialized mucosa on the tongue?

Sulcus terminalis

What is the foramen cecum?

Small depression in the middle of the sulcus terminalis on the tongue

What are the two main regions of the respiratory system?

Conducting portion and respiratory portion

What is the function of the conducting portion?

Brings air from outside to the site of respiration, conditions air, senses smell, and produces speech

What structures make up the conducting portion?

Nose, nasopharynx, larynx, trachea, bronchi, terminal bronchioles

What is the function of the respiratory portion?

Gas exchange and oxygenation of the blood

What structures make up the respiratory portion?

Respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli

What is the first entryway for air into the respiratory system?

Nasal cavities

What separates the two nasal cavities?

Nasal septum

What are the two parts of the nasal cavity?

Vestibule and nasal fossa

What is the function of the nasal vestibule?

Conditions air and acts as a coarse filter via vibrissae

What are vibrissae?

Short hairs in the vestibule that trap large particulates

What surrounds the vestibule?

Cartilage, outside the skull

What is the nasal fossa?

Larger cavity inside the skull for air conditioning

What structures increase surface area in the nasal fossa?

Conchae (turbinates)

How do conchae aid air conditioning?

Increase surface area and create swirling airflow for longer air contact

What are venous plexus or swell bodies in the nasal fossa?

Branching networks of blood vessels beneath the epithelium

What is the function of swell bodies?

Periodically engorge with blood every 20–30 min, shunting airflow to the other nasal cavity and protecting epithelium from drying

How does blood flow in the nasal fossa relative to air flow?

Counter-current system (blood flows back-to-front while air flows front-to-back)

What is the function of the counter-current blood flow?

Increases efficiency of air conditioning by warming/cooling air

What epithelium lines the vestibule?

Non-keratinized stratified squamous epithelium

Why is the vestibule epithelium transitional?

Changes from skin to respiratory epithelium

What epithelium lines the nasal fossa?

Typical respiratory epithelium (ciliated pseudostratified columnar)

What are the five cell types in typical respiratory epithelium?

Ciliated columnar cells, goblet cells, brush cells, small granule (Kulchitsky) cells, basal cells

What is the function of ciliated columnar cells?

Move mucus and trapped particles out of airways

What disorder is associated with immotile cilia?

Kartagener’s syndrome (dynein deficiency)

What is the function of goblet cells?

Produce mucus

What is the function of brush cells?

Sensory cells that sense the condition of the epithelium and connect to trigeminal nerve

What is the function of small granule (Kulchitsky) cells?

Part of DNES, secrete hormones or catecholamines (epinephrine, norepinephrine, dopamine)

What are the two populations of Kulchitsky cells based on secretion?

Small molecules (catecholamines, APUD) and large molecules (serotonin, peptide hormones)

What is paracrine secretion?

Localized effect on nearby cells in the respiratory system

What is endocrine secretion?

Hormones transported via the blood to act on distant cells

What is the function of basal cells in respiratory epithelium?

Stem cells for the epithelium

What is the exception to typical respiratory epithelium in the nasal cavity?

Olfactory epithelium

Where is olfactory epithelium located?

Superior turbinate and roof of nasal fossa

What type of epithelium is olfactory epithelium?

Pseudostratified columnar

What are the four cell types in olfactory epithelium?

Olfactory cells, sustentacular cells, basal cells, brush cells

What is the function of olfactory cells?

Sensory bipolar neurons that detect odors

What structures of olfactory cells reach the apical surface?

Dendrites with non-motile cilia containing odorant receptors

Where do olfactory cell axons go?

Penetrate basement membrane and form fibers of the olfactory nerve

What is the function of sustentacular cells?

Support olfactory cells physically and metabolically; produce odorant-binding protein

What is the function of basal cells in olfactory epithelium?

Stem cells to replace all epithelial cell types including neurons

What are Bowman’s glands and their function?

Serous acini under epithelium; secrete continuous watery fluid to dissolve odorants and keep surface clean

What are exceptions to respiratory epithelium in the larynx?

Epiglottis and vocal cords

What epithelium type covers epiglottis and vocal cords?

Non-keratinized stratified squamous

What is the structure and function of the trachea?

~10 inches long, rigid tube held open by C-shaped hyaline cartilage rings; conducts air to bronchi

What happens at the end of the trachea?

Divides into two primary bronchi

What defines a bronchiole?

Airway division without cartilage

What epithelium lines airways from trachea to bronchioles?

Typical respiratory epithelium

What is the primary function of the respiratory tree?

Conduct air and eventually perform gas exchange

What are terminal bronchioles?

Last part of the conducting portion

What changes occur in terminal bronchiole epithelium?

Ciliated simple columnar cells replace pseudostratified columnar

What are club cells and their function?

Dome-shaped, non-ciliated cells; secrete surface-active lipoprotein (reduces surface tension) and CC16 (protects airway lining and regulates inflammation)

Are goblet cells present in terminal bronchioles?

Normally absent; may appear due to metaplasia from smoking

What controls smooth muscle in terminal bronchioles?

Vagus nerve (parasympathetic) causes contraction; sympathetic causes relaxation

What happens in respiratory bronchioles?

Terminal bronchioles divide; epithelium is similar except interrupted by alveolar outpocketings

What is alveolar epithelium composed of?

Type I pneumocytes, Type II pneumocytes, brush cells, dust cells

What percentage of alveolar surface do Type I pneumocytes cover?

97%