Bone Morphogenetic Protein Receptors, Type II: A subtype of bone morphogenetic protein receptors with low affinity for BONE MORPHOGENETIC PROTEINS. They are constitutively active PROTEIN-SERINE-THREONINE KINASES that can interact with and phosphorylate TYPE I BONE MORPHOGENETIC PROTEIN RECEPTORS.Bone Morphogenetic Protein Receptors, Type I: A subtype of bone morphogenetic protein receptors with high affinity for BONE MORPHOGENETIC PROTEINS. They can interact with and undergo PHOSPHORYLATION by BONE MORPHOGENETIC PROTEIN RECEPTORS, TYPE II. They signal primarily through RECEPTOR-REGULATED SMAD PROTEINS.Hypertension, Pulmonary: Increased VASCULAR RESISTANCE in the PULMONARY CIRCULATION, usually secondary to HEART DISEASES or LUNG DISEASES.Bone Morphogenetic Protein Receptors: A family of CELL SURFACE RECEPTORS that bind BONE MORPHOGENETIC PROTEINS. They are PROTEIN-SERINE-THREONINE KINASES that mediate SIGNAL TRANSDUCTION PATHWAYS through SMAD PROTEINS.Bone Morphogenetic Proteins: Bone-growth regulatory factors that are members of the transforming growth factor-beta superfamily of proteins. They are synthesized as large precursor molecules which are cleaved by proteolytic enzymes. The active form can consist of a dimer of two identical proteins or a heterodimer of two related bone morphogenetic proteins.Bone Morphogenetic Protein 2: A potent osteoinductive protein that plays a critical role in the differentiation of osteoprogenitor cells into OSTEOBLASTS.Smad1 Protein: A receptor-regulated smad protein that undergoes PHOSPHORYLATION by BONE MORPHOGENETIC PROTEIN RECEPTORS. It regulates BONE MORPHOGENETIC PROTEIN signaling and plays an essential role in EMBRYONIC DEVELOPMENT.Bone Morphogenetic Protein 4: A bone morphogenetic protein that is a potent inducer of bone formation. It also functions as a regulator of MESODERM formation during EMBRYONIC DEVELOPMENT.Receptors, Growth Factor: Cell surface receptors that bind growth or trophic factors with high affinity, triggering intracellular responses which influence the growth, differentiation, or survival of cells.Smad Proteins, Receptor-Regulated: A family of smad proteins that undergo PHOSPHORYLATION by CELL SURFACE RECEPTORS in response to TRANSFORMING GROWTH FACTOR BETA; ACTIVIN; or BONE MORPHOGENETIC PROTEIN signaling.Receptors, Transforming Growth Factor beta: Cell-surface proteins that bind transforming growth factor beta and trigger changes influencing the behavior of cells. Two types of transforming growth factor receptors have been recognized. They differ in affinity for different members of the transforming growth factor beta family and in cellular mechanisms of action.Bone Morphogenetic Protein 7: A bone morphogenetic protein that is widely expressed during EMBRYONIC DEVELOPMENT. It is both a potent osteogenic factor and a specific regulator of nephrogenesis.Smad Proteins: A family of proteins that are involved in the translocation of signals from TGF-BETA RECEPTORS; BONE MORPHOGENETIC PROTEIN RECEPTORS; and other surface receptors to the CELL NUCLEUS. They were originally identified as a class of proteins that are related to the mothers against decapentaplegic protein, Drosophila and sma proteins from CAENORHABDITIS ELEGANS.Activin Receptors, Type II: One of the two types of ACTIVIN RECEPTORS. They are membrane protein kinases belonging to the family of PROTEIN-SERINE-THREONINE KINASES. The major type II activin receptors are ActR-IIA and ActR-IIB.Activin Receptors, Type I: One of the two types of ACTIVIN RECEPTORS or activin receptor-like kinases (ALK'S). There are several type I activin receptors. The major active ones are ALK-2 (ActR-IA) and ALK-4 (ActR-IB).Transforming Growth Factor beta: A factor synthesized in a wide variety of tissues. It acts synergistically with TGF-alpha in inducing phenotypic transformation and can also act as a negative autocrine growth factor. TGF-beta has a potential role in embryonal development, cellular differentiation, hormone secretion, and immune function. TGF-beta is found mostly as homodimer forms of separate gene products TGF-beta1, TGF-beta2 or TGF-beta3. Heterodimers composed of TGF-beta1 and 2 (TGF-beta1.2) or of TGF-beta2 and 3 (TGF-beta2.3) have been isolated. The TGF-beta proteins are synthesized as precursor proteins.Protein-Serine-Threonine Kinases: A group of enzymes that catalyzes the phosphorylation of serine or threonine residues in proteins, with ATP or other nucleotides as phosphate donors.Signal Transduction: The intracellular transfer of information (biological activation/inhibition) through a signal pathway. In each signal transduction system, an activation/inhibition signal from a biologically active molecule (hormone, neurotransmitter) is mediated via the coupling of a receptor/enzyme to a second messenger system or to an ion channel. Signal transduction plays an important role in activating cellular functions, cell differentiation, and cell proliferation. Examples of signal transduction systems are the GAMMA-AMINOBUTYRIC ACID-postsynaptic receptor-calcium ion channel system, the receptor-mediated T-cell activation pathway, and the receptor-mediated activation of phospholipases. Those coupled to membrane depolarization or intracellular release of calcium include the receptor-mediated activation of cytotoxic functions in granulocytes and the synaptic potentiation of protein kinase activation. Some signal transduction pathways may be part of larger signal transduction pathways; for example, protein kinase activation is part of the platelet activation signal pathway.Receptors, Interleukin-1 Type II: An interleukin-1 receptor subtype that competes with the INTERLEUKIN-1 RECEPTOR TYPE I for binding to INTERLEUKIN-1ALPHA and INTERLEUKIN-1BETA. The interleukin-1 type II receptor appears to lack signal transduction capability. Therefore it may act as a "decoy" receptor that modulates the activity of its ligands. Both membrane-bound and soluble forms of the receptor have been identified.Bone Morphogenetic Protein 6: A bone morphogenetic protein that is a potent inducer of BONE formation. It plays additional roles in regulating CELL DIFFERENTIATION of non-osteoblastic cell types and epithelial-mesenchymal interactions.Pulmonary Artery: The short wide vessel arising from the conus arteriosus of the right ventricle and conveying unaerated blood to the lungs.