Anatomy of the Glandular Stomach and Nasal Structure

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The craniodorsal blind sac opens in the glandular stomach ______ and with the duodenum on the right side.

cranially

The craniodorsal blind sac opens with the ______ on the right side.

duodenum

On the surface of the epithelium is a hardened membrane called ______.

cuticule

The internal surface of the craniodorsal blind sac includes a hardened membrane known as ______.

cuticule Signup and view all the answers

The craniodorsal blind sac is located in the ______ stomach.

glandular Signup and view all the answers

The caudal nasal concha is a hollow ______.

mound Signup and view all the answers

The caudal nasal concha is absent in some ______.

birds Signup and view all the answers

The caudal nasal concha connects to the ______ sinus.

infraorbital Signup and view all the answers

The caudal nasal concha is lined by ______ epithelium.

olfactory Signup and view all the answers

The caudal nasal concha does not connect to the nasal ______.

cavity Signup and view all the answers

The nasal cavity is lined by ______ epithelium rostrally.

stratified squamous Signup and view all the answers

Caudally, the nasal cavity is lined by ______ respiratory epithelium.

mucociliary Signup and view all the answers

The nasal gland consists of two lobes: medial and ______.

lateral Signup and view all the answers

Each lobe of the nasal gland opens in the ______ of the nasal cavity.

vestibule Signup and view all the answers

The nasal gland may be ______ in a few species.

absent Signup and view all the answers

It opens ventrally to oropharynx through the ______ slit.

choanal Signup and view all the answers

The nasal cavity opens rostrally to the exterior through the ______.

nostrils Signup and view all the answers

One of the general functions of the nasal cavity is ______.

olfaction Signup and view all the answers

The nasal cavity is responsible for the ______ of airborne particles.

filtration Signup and view all the answers

The nasal cavity also plays a role in the ______ of inspired air.

humidification Signup and view all the answers

It lies at the bifurcation of the ______.

trachea Signup and view all the answers

Types of syrinx can be classified according to the origin of its ______.

cartilages Signup and view all the answers

The first type of syrinx is ______.

Tracheal Signup and view all the answers

The majority of birds have a ______ syrinx.

Tracheobronchial Signup and view all the answers

The liver lies on each side of the ______.

heart Signup and view all the answers

The dorsal border runs parallel to the ______ column.

vertebral Signup and view all the answers

In the cranial part of the body cavity, the liver is in a ______ position.

dorsal Signup and view all the answers

The liver and not the lung is found in the ______ position in this structure.

mammals Signup and view all the answers

The liver's position can be described as lying in the roof of the ______ cavity.

body Signup and view all the answers

Study Notes

Avian Anatomy Overview

Avian anatomy refers to the structural make-up of birds.

Digestive System

The avian digestive system has 3 main components.
1.Oral cavity and pharynx: Lack of a soft palate and glossoplatine arch combine to form a single cavity. No lips or teeth; beaks are used instead. Oral opening is the entrance to the oral cavity.
2.Alimentary tract: Includes various organs like esophagus, crop, proventriculus, gizzard, small intestine (duodenum, jejunum, ileum), large intestine (paired ceca, colon or rectum), and cloaca.Accessory glands such as salivary glands, liver, and pancreas play vital roles.
3.Accessory Glands: include salivary glands, liver, and pancreas.
Different bird types have varying beak shapes depending on their diet.
Examples of varying beak appearance
Fowl and Pigeon have pointed beaks with hard, rigid sheaths. Upper beak often projects beyond the lower beak.
Ducks and geese have blunt, spoon-like beaks with a flexible horny sheath called ceroma covering the beak. The horny sheath may resemble finger nails in structure. Also, they have honey lamellae along the upper and lower beaks.
The roof of the oral cavity is formed from an incomplete hard palate. It communicates with the nasal cavity through choanae (coanal cleft or slit). Choanae lies in the midline of the caudal half of the palate, connecting the oropharynx and nasal cavity. Its mucosa has palatine ridges and papillae.
Palatine ridges are three in number: median palatine ridges on the rostral part of the palate, and two lateral palatine ridges positioned laterally from the median ridge.
Palatine papillae are arranged in five rows, directed caudally, close to the midline. They have two rows rostral to the choanae, two rows on each side of the narrow part of the choana, and one caudal row at the junction of the narrow and wide parts of the choana. Small papillae are irregularly distributed on the palate.
Palate submucosa include paired maxillary, medial palatine, and lateral palatine salivary glands.
Cheeks are the lateral walls of the oral cavity. Their submucosa contains salivary glands.
The floor of the oral cavity is covered by the tongue. The submucosa contains paired mandibular salivary glands.

Tongue

The tongue has different types and functions based on the species and its diet (shape, function, and fixation)
It is long and protrusible for collecting food. It is thicker and non-protrusible for moving ingested material (swallowing). The shape varies based on the lower beak. Fixed by the hyobranchial apparatus and the fraenulum linguae (tongue attachment).

Structure Analysis

The structure of the tongue includes the apex, body, and root. It exhibits a median groove on the dorsal surface, with transverse rows of lingual papillae between the body and root. Extrinsic muscles are present on the entire tongue except for the apex. Microscopically, it lacks internal muscles but consists of connective tissue, adipose tissue, and glands. The lamina propria has lingual salivary glands. Birds have significantly fewer taste buds compared to mammals.

Pharynx

Roof of pharynx is divided by an infundibular slit, with papillae on the mucous membrane. The submucosa contains sphenopterygoid salivary glands. The floor of the pharynx is formed by the root of the tongue rostrally. The caudal part features a laryngeal mound. Submucosa contains submandibular and cricoarytenoid glands.

Salivary Glands

Well-developed salivary glands are common in birds with dry diets but absent in a few bird species. They secrete mucous saliva, which acts as a lubricant during swallowing. There are different classifications of salivary glands based on their opening sites into the mouth cavity or pharyngeal cavity, and on the number of openings..

Esophagus

The esophagus is a thin-walled, extensible tube with a large diameter. It connects the pharyngeal cavity to the stomach. Divided into a longer cervical section and a shorter thoracic section.The cervical part is located midline dorsal to the larynx and trachea, descending caudally to the fifth cervical vertebrae, and angling to the right side of the neck.
The portion of the esophagus that is cranial to the thoracic inlet transitions to the midline and then expands ventrally to form the crop.
The crop is a distensible diverticulum of the esophagus that stores food for a short time. Its shape varies based on the species: domestic fowl have a thin-walled sac attached to the skin. Pigeons have two large lateral sacs, while aquatic birds (duck and goose) have a simple spindle shape (and no true crop structures).
The thoracic part is shorter than the cervical part and extends caudally within the thorax, dorsal to the trachea and the base of the heart. It terminates at the glandular stomach and is surrounded by cervical and clavicular air sacs. The esophagus's major functions include transporting food and being a site of physical digestion, as well as crop milk formation.

Crop Milk

Crop milk is produced by regurgitation in pigeons and doves, fed to their young by both sexes. It is produced by desquamation of fat-laden cells in the epithelium. Epithelial proliferation occurs at the sixth day of incubation, followed by secretion at the sixteenth day of incubation and continuing up to two weeks after hatching. The composition of crop milk is similar to mammalian milk, rich in fats and proteins, and lacking carbohydrates and calcium.

Stomach

The stomach is composed of two parts:
1. Glandular stomach (proventriculus) – Produces gastric juices (acid and proteolytic enzymes). Elongated spindle shape; it continues with the esophagus, with a distinct constriction (isthmus) at the junction with the muscular stomach. Located in the lower left quadrant of the body cavity, causing a depression on the dorsal surface of the liver. Wall is thicker than that of the esophagus, lined with simple columnar epithelium, with compound tubular glands opening onto papillae of the mucous membrane.
1. Muscular stomach (ventriculus or gizzard) –
- Function: a "masticatory" organ, it mechanically grinds food via powerful muscle contractions, thick internal tunica cuticula (a hardened membrane), folds, and the presence of stones within the lumen.
- Shape: somewhat lens-like, and red and firm. The craniocaudal diameter is greater than the dorsoventral one. Positional relation: It fills the left lower quadrant of the body cavity; it has contact with the sternum and the left lateral abdominal wall.
- Description: the body is the main, thick-walled part of the gizzard. Two blind sacs with thin walls: a) craniodorsal sac, and b) caudoventral sac. The craniodorsal sac opens into the glandular stomach cranially and the duodenum on the right side. Structure: the inner surface of the gizzard has a hardened membrane called the cuticula, produced by glands and the surface epithelium. It has folds, which become thinner over the blind sacs. The cuticula is usually brown, green, or yellow due to regurgitated bile pigment from the duodenum, and often worn down due to grinding movements. Muscles: Four smooth muscles attached to glistening, right and left tendinous aponeuroses (or tendinous center). These consist of 1) two thick lateral muscles (dorsal and ventral) of the body, and 2) two thin intermediate muscles (craniodorsal and caudoventral) of the blind sacs.

Intestinal Tract

1. Small intestine (duodenum, jejunum, ileum)
1. Large intestine (paired ceca, colon or rectum)
The duodenum, arising from the right surface of the gizzard, forms a U-shaped loop with an ascending and descending limb. The pancreas lies between these two limbs.
It is fixed by a pancreaticoduodenal fold and ligaments (suspensory and hepatoduodenal) to the gizzard and liver; the bile and pancreatic ducts open into the ascending duodenum with two or three ducts arising from the liver and the pancreas. The lumen of the duodenum is wider than that of the stomach.
The jejunum is the longest part of the small intestine, exhibiting loose coils along the long mesentery. Proximal and distal parts are nearly straight; however, the overall jejunum usually appears as loose coils in fowls, and U-shaped loops in ducks and geese, and a cone shape in pigeons. Vitelline diverticulum or Meckel's diverticulum is present.
1. Ileum is yellowish to reddish-gray. Flanked by right and left ceca, connected by the ileoceal ligament. It is continuous with the rectum caudally, with a small constriction. It begins at the vitelline diverticulum or opposite the apices of the ceca.
4.Cecum: In most birds, two ceca arise at the junction between the ileum and rectum. Some birds only have one cecum. It is absent in carnivorous birds and parrots. The ceca are well-developed in fowl, ducks, and geese, while in pigeons, they are very short and appear as bud-like appendages to the colon. Each cecum has a base, body, and apex. The base and apex are light red, while the body is bluish-green to grayish-green in color. The base has a thick wall due to a heavy muscle coat (cecal sphincter) and much lymphoid tissue (cecal tonsil).
1. Colon or Rectum is a light gray-to-green continuation of the ileum, located caudal to the vertebral column and ending at the coprodaeum of the cloaca. Suspended by a short mesentery from the dorsal wall of the abdominal cavity, continuous with that of the ileum.

Accessory Glands

The liver is important as a vital accessory gland in the bird digestive system. Its size, weight, consistency, and color vary based on the bird's breed, age, and nutritional status.

-Color: Young birds have a yellow liver due to pigments from yolk assimilation during incubation. Old birds have a dark-brown liver. -Lobation: The liver consists of a right and left lobe. The right lobe is heart-shaped and larger, containing the gall bladder on its visceral surface and perforated by the caudal vena cava. The left lobe is smaller and prismatic in shape, divided by fissure into caudo-dorsal and caudo-ventral parts. -Surfaces: Visceral (dorsal) surface of the liver is uneven and concave, with several impressions. Parietal (ventral) surfaces is smooth and convex, but the cranioventral portion is concave to accommodate the apex of the heart. -Border: The liver has sharp lateral and caudal borders and a blunt medial border.
The biliary ducts are separate and drain into the ascending duodenum, with two ducts from the liver and two or three from the pancreas in fowls.
The pancreatic structure and the pancreatic secretions are described. The pancreas has exocrine and endocrine portions. The exocrine portion drains into the ascending duodenum via pancreatic ducts. The endocrine portion comprises islets of Langerhans, which secrete glucagon and insulin.

Spleen

An important blood-forming organ
Located on the right surface at the junction of the proventriculus and the gizzard. Birds have different splenic structures based on the species.
In fowl, it is brownish-red rounded or oval shaped.
In duck and geese, it is triangular with a flat dorsal and a convex ventral surface.
In pigeons, it is oval and elongated.

Respiratory System

The respiratory system functions in gas exchange, eliminating heat, and in voice production. Components are nasal cavity, larynx, trachea, syrinx, lungs, and air sacs. -Nasal cavity: Cone-shaped; opens ventrally to oropharynx through the choanal slit; opens rostrally through the nostrils. Functions include olfaction, filtration of airborne particles, and humidification of inspired air. The nostrils are elongated slits at the base of the upper beak and dorsally overlapped by an operculum in fowl and turkeys. They may also be feathered or completely closed. There are distinct regions, including a rostral vestibule, respiratory regions, and an olfactory region, each with its own conchae. The nasal septum divides the cavity and is mostly cartilaginous or partially bony, sometimes perforated rostrally in aquatic birds.
Larynx: Located on the floor of the pharyngeal cavity. The laryngeal inlet (glottis) is a narrow slit, supported by arytenoid cartilages. The larynx skeleton consists of four cartilages: cricoid, procricoid, and paired arytenoid cartilages. Thyroid and epiglottic cartilages are absent. The laryngeal mound holds the larynx. It has four rows of papillae (caudal): a rostral transverse row, a caudal transverse row, and two sagittal rows of small papillae.
Trachea: Is comprised of cartilaginous rings. The rings are complete, not C-shaped like in mammals. The first and last four rings are simple, while the others are shaped like signet rings. The broad part of the successive rings overlap the narrow parts of adjacent rings externally, joined by anular ligaments..
Trachea course: Cranial end lies midline ventral to the esophagus and after 3-5cm moves to the right side. Entering the thoracic inlet, it returns to the midline ventral to the esophagus and above the heart before dividing into two main bronchi.
Syrinx: is the voice organ; at the bifurcation of the trachea. It is classified as tracheal, tracheobronchial, or bronchial based on its origin. Syrinx structure features hard and soft components. Hard structures consist of four cartilages, and soft structures include pairs of vibrating membranes.
Lungs and air sacs: The lungs are located dorsally within the cranial part of the body cavity. They and the liver are positioned on either side of the heart. Lungs have no lobes like in mammals. Anatomical features such as their borders and lung surfaces (dorsal, dorsomedial, and ventromedial) are discussed. -The three pairs of primary (main) bronchi enter hilus, extend, and reach the caudal extremity of the lung. -Several pairs of secondary bronchi are named based on the regions they supply (e.g. medioventrally, mediadorsally, lateroventrally, laterodorsally.
- Many small, uniform, and freely anastomosing tubes called parabronchi branch off from the mediodorsal secondary bronchi.
Air sacs are thin-walled structures connected to the lungs. They help reduce body weight, regulate body temperature, and are involved in voice production. There are multiple air sacs in birds; eight (8) in adults: cervical, clavicular, cranial thoracic, caudal thoracic, and abdominal. The sacs are classified anatomically, describing their shape and position. For example, the cervical air sac consists of a primary chamber and two diverticula.

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This quiz covers key concepts related to the anatomy of the glandular stomach and nasal structures, including the craniodorsal blind sac and caudal nasal concha. Test your knowledge on their functions, connections, and epithelial linings. Perfect for veterinary students or those interested in animal anatomy.